Fair Value Measurement - Summary of Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	$ 387,786	$ 399,680
Gross Unrealized Gains (Losses)	(18,354)	1,491
Recorded Basis	369,432	401,171
Investments Current [Member] | Cash and Cash Equivalents [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	29,439	13,384
Recorded Basis	29,439	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	29,439	13,384
Recorded Basis	29,439	13,384
Investments Current [Member] | Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	86,069	96,959
Gross Unrealized Gains (Losses)	(4,735)	(196)
Recorded Basis	81,334	96,763
Investments Current [Member] | Investments [Member] | Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	41,899	41,954
Gross Unrealized Gains (Losses)	(2,912)	(136)
Recorded Basis	38,987	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	19,521	29,533
Gross Unrealized Gains (Losses)	(220)	(38)
Recorded Basis	19,301	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	17,270	18,089
Gross Unrealized Gains (Losses)	(1,588)	(440)
Recorded Basis	15,682	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	7,379	7,383
Gross Unrealized Gains (Losses)	(15)	418
Recorded Basis	7,364	7,801
Investments Noncurrent [Member] | Restricted Cash and Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	272,278	289,337
Gross Unrealized Gains (Losses)	(13,619)	1,687
Recorded Basis	258,659	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	427	528
Recorded Basis	427	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	107,011	117,700
Gross Unrealized Gains (Losses)	(5,914)	(17)
Recorded Basis	101,097	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	66,525	67,614
Gross Unrealized Gains (Losses)	(4,505)	(342)
Recorded Basis	62,020	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	77	107
Gross Unrealized Gains (Losses)		1
Recorded Basis	77	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	58,378	64,217
Gross Unrealized Gains (Losses)	(2,491)	764
Recorded Basis	55,887	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	32,868	32,898
Gross Unrealized Gains (Losses)	(709)	1,281
Recorded Basis	32,159	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	6,992	6,273
Recorded Basis	$ 6,992	$ 6,273