Fair Value Measurement - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	$ 321,807	$ 365,364
Other [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	36,530	64,572
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	3,514	3,466
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	281,763	297,326
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	2,135	35,526
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	2,135	35,526
Investments [Member] | Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	36,154	53,649
Investments [Member] | Corporate Bonds [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	36,154	53,649
Investments [Member] | Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	370	2,738
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	370	2,738
Investments [Member] | U.S. Treasuries [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	2,465	4,509
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	2,465	4,509
Investments [Member] | U.S. Government Agency Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	7,829	7,690
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	7,829	7,690
Investments [Member] | Asset Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	32,555	14,004
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	32,555	14,004
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	34,395	29,046
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	34,395	29,046
Restricted Cash and Investments [Member] | Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	101,081	100,412
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	101,081	100,412
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	61,939	63,767
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	61,939	63,767
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	7,334	16,927
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	7,334	16,927
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	26,905	28,527
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	26,905	28,527
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	289	303
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	289	303
Restricted Cash and Investments [Member] | Mutual Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	3,514	3,466
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	3,514	3,466
Restricted Cash and Investments [Member] | Supranational Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Recorded Basis	4,842	4,800
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	$ 4,842	$ 4,800