Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurement - Summary of Assets Measured at Fair Value on Recurring Basis (Detail)

v3.19.3
Fair Value Measurement - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis $ 353,758 $ 365,948
Other [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 25,204 449
Level 1 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 2,844 1,093
Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 325,710 364,406
Cash and Cash Equivalents [Member] | Money Market Funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 6,121 30
Cash and Cash Equivalents [Member] | Money Market Funds [Member] | Other [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 6,121 30
Investments [Member] | Corporate Bonds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 70,958 435
Investments [Member] | Corporate Bonds [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 70,958 435
Investments [Member] | Mortgage Backed Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 2,935 471
Investments [Member] | Mortgage Backed Securities [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 2,935 471
Investments [Member] | U.S. Treasuries [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 18,615 1,138
Investments [Member] | U.S. Treasuries [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 18,615 1,138
Investments [Member] | U.S. Government Agency Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 9,223 49
Investments [Member] | U.S. Government Agency Securities [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 9,223 49
Investments [Member] | Asset Backed Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 17 10
Investments [Member] | Asset Backed Securities [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 17 10
Restricted Cash and Investments [Member] | Money Market Funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 19,083 419
Restricted Cash and Investments [Member] | Money Market Funds [Member] | Other [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 19,083 419
Restricted Cash and Investments [Member] | Corporate Bonds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 103,326 181,377
Restricted Cash and Investments [Member] | Corporate Bonds [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 103,326 181,377
Restricted Cash and Investments [Member] | Mortgage Backed Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 66,519 87,400
Restricted Cash and Investments [Member] | Mortgage Backed Securities [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 66,519 87,400
Restricted Cash and Investments [Member] | U.S. Treasuries [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 18,421 44,021
Restricted Cash and Investments [Member] | U.S. Treasuries [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 18,421 44,021
Restricted Cash and Investments [Member] | U.S. Government Agency Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 30,727 44,640
Restricted Cash and Investments [Member] | U.S. Government Agency Securities [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 30,727 44,640
Restricted Cash and Investments [Member] | Asset Backed Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 117 74
Restricted Cash and Investments [Member] | Asset Backed Securities [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 117 74
Restricted Cash and Investments [Member] | Mutual Funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 2,844 1,093
Restricted Cash and Investments [Member] | Mutual Funds [Member] | Level 1 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 2,844 1,093
Restricted Cash and Investments [Member] | Supranational Bonds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 4,802 4,741
Restricted Cash and Investments [Member] | Supranational Bonds [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 4,802 4,741
Restricted Cash and Investments [Member] | Municipal Bonds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis 50 50
Restricted Cash and Investments [Member] | Municipal Bonds [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Recorded Basis $ 50 $ 50