Fair Value Measurement - Summary of Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	$ 346,087	$ 399,680
Gross Unrealized Gains (Losses)	(38,140)	1,491
Recorded Basis	307,947	401,171
Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	77,746	96,959
Gross Unrealized Gains (Losses)	(9,421)	(196)
Recorded Basis	68,325	96,763
Restricted Cash and Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	228,045	289,337
Gross Unrealized Gains (Losses)	(28,719)	1,687
Recorded Basis	199,326	291,024
Money Market Funds [Member] | Cash and Cash Equivalents [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	40,296	13,384
Recorded Basis	40,296	13,384
Money Market Funds [Member] | Restricted Cash and Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	646	528
Recorded Basis	646	528
Corporate Bonds [Member] | Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	38,489	41,954
Gross Unrealized Gains (Losses)	(5,181)	(136)
Recorded Basis	33,308	41,818
Corporate Bonds [Member] | Restricted Cash and Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	81,993	117,700
Gross Unrealized Gains (Losses)	(11,296)	(17)
Recorded Basis	70,697	117,683
U.S. Treasuries [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	66,479	67,614
Gross Unrealized Gains (Losses)	(9,222)	(342)
Recorded Basis	57,257	67,272
Asset Backed Securities [Member] | Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	13,709	29,533
Gross Unrealized Gains (Losses)	(737)	(38)
Recorded Basis	12,972	29,495
Asset Backed Securities [Member] | Restricted Cash and Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	9	107
Gross Unrealized Gains (Losses)		1
Recorded Basis	9	108
U.S. Government Agency Securities [Member] | Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	7,369	7,383
Gross Unrealized Gains (Losses)	(302)	418
Recorded Basis	7,067	7,801
U.S. Government Agency Securities [Member] | Restricted Cash and Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	26,479	32,898
Gross Unrealized Gains (Losses)	(2,156)	1,281
Recorded Basis	24,323	34,179
Mortgage Backed Securities [Member] | Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	16,135	18,089
Gross Unrealized Gains (Losses)	(3,139)	(440)
Recorded Basis	12,996	17,649
Mortgage Backed Securities [Member] | Restricted Cash and Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	46,138	64,217
Gross Unrealized Gains (Losses)	(6,045)	764
Recorded Basis	40,093	64,981
Emerging Markets [Member] | Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	2,044
Gross Unrealized Gains (Losses)	(62)
Recorded Basis	1,982
Mutual Funds [Member] | Restricted Cash and Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	6,301	6,273
Recorded Basis	6,301	6,273
Marketable Securities Current [Member] | Cash and Cash Equivalents [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	40,296	13,384
Recorded Basis	$ 40,296	$ 13,384