Fair Value Measurement - Summary of Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	$ 367,135	$ 399,680
Gross Unrealized Gains (Losses)	(30,269)	1,491
Recorded Basis	336,866	401,171
Investments Current [Member] | Cash and Cash Equivalents [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	29,587	13,384
Recorded Basis	29,587	13,384
Investments Current [Member] | Cash and Cash Equivalents [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	29,587	13,384
Recorded Basis	29,587	13,384
Investments Current [Member] | Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	85,422	96,959
Gross Unrealized Gains (Losses)	(8,119)	(196)
Recorded Basis	77,303	96,763
Investments Current [Member] | Investments [Member] | Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	39,720	41,954
Gross Unrealized Gains (Losses)	(4,739)	(136)
Recorded Basis	34,981	41,818
Investments Current [Member] | Investments [Member] | Asset Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	19,509	29,533
Gross Unrealized Gains (Losses)	(806)	(38)
Recorded Basis	18,703	29,495
Investments Current [Member] | Investments [Member] | Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	16,753	18,089
Gross Unrealized Gains (Losses)	(2,470)	(440)
Recorded Basis	14,283	17,649
Investments Current [Member] | Investments [Member] | U.S. Government Agency Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	7,376	7,383
Gross Unrealized Gains (Losses)	(58)	418
Recorded Basis	7,318	7,801
Investments Current [Member] | Investments [Member] | Emerging Markets [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	2,064
Gross Unrealized Gains (Losses)	(46)
Recorded Basis	2,018
Investments Noncurrent [Member] | Restricted Cash and Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	252,126	289,337
Gross Unrealized Gains (Losses)	(22,150)	1,687
Recorded Basis	229,976	291,024
Investments Noncurrent [Member] | Restricted Cash and Investments [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	597	528
Recorded Basis	597	528
Investments Noncurrent [Member] | Restricted Cash and Investments [Member] | Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	93,129	117,700
Gross Unrealized Gains (Losses)	(9,578)	(17)
Recorded Basis	83,551	117,683
Investments Noncurrent [Member] | Restricted Cash and Investments [Member] | U.S. Treasuries [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	66,252	67,614
Gross Unrealized Gains (Losses)	(6,774)	(342)
Recorded Basis	59,478	67,272
Investments Noncurrent [Member] | Restricted Cash and Investments [Member] | Asset Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	51	107
Gross Unrealized Gains (Losses)		1
Recorded Basis	51	108
Investments Noncurrent [Member] | Restricted Cash and Investments [Member] | Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	54,255	64,217
Gross Unrealized Gains (Losses)	(4,595)	764
Recorded Basis	49,660	64,981
Investments Noncurrent [Member] | Restricted Cash and Investments [Member] | U.S. Government Agency Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	31,857	32,898
Gross Unrealized Gains (Losses)	(1,203)	1,281
Recorded Basis	30,654	34,179
Investments Noncurrent [Member] | Restricted Cash and Investments [Member] | Mutual Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	5,985	6,273
Recorded Basis	$ 5,985	$ 6,273