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Fair Value Measurement - Summary of Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	$ 399,680	$ 363,671
Gross Unrealized Gains (Losses)	1,491	10,450
Recorded Basis	401,171	374,121
Investments Current [Member] | Cash and Cash Equivalents [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	13,384	42,007
Recorded Basis	13,384	42,007
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	13,384	42,007
Recorded Basis	13,384	42,007
Investments Current [Member] | Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	96,959	99,729
Gross Unrealized Gains (Losses)	(196)	1,515
Recorded Basis	96,763	101,244
Investments Current [Member] | Investments [Member] | Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	41,954	50,918
Gross Unrealized Gains (Losses)	(136)	884
Recorded Basis	41,818	51,802
Investments Current [Member] | Investments [Member] | Asset Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	29,533	36,948
Gross Unrealized Gains (Losses)	(38)	(146)
Recorded Basis	29,495	36,802
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	7,383	7,396
Gross Unrealized Gains (Losses)	418	752
Recorded Basis	7,801	8,148
Investments Current [Member] | Investments [Member] | Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	18,089	4,367
Gross Unrealized Gains (Losses)	(440)	24
Recorded Basis	17,649	4,391
Investments Current [Member] | Investments [Member] | U.S. Treasuries [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost		100
Gross Unrealized Gains (Losses)		1
Recorded Basis		101
Investments Noncurrent [Member] | Restricted Cash and Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost	289,337	221,935
Gross Unrealized Gains (Losses)	1,687	8,935
Recorded Basis	291,024	230,870
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	528	40,063
Gross Unrealized Gains (Losses)		(4)
Recorded Basis	528	40,059
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	117,700	88,902
Gross Unrealized Gains (Losses)	(17)	4,091
Recorded Basis	117,683	92,993
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	107	256
Gross Unrealized Gains (Losses)	1	4
Recorded Basis	108	260
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	32,898	29,737
Gross Unrealized Gains (Losses)	1,281	2,466
Recorded Basis	34,179	32,203
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	64,217	48,795
Gross Unrealized Gains (Losses)	764	2,356
Recorded Basis	64,981	51,151
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	67,614	4,371
Gross Unrealized Gains (Losses)	(342)	19
Recorded Basis	67,272	4,390
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	6,273	5,036
Recorded Basis	$ 6,273	5,036
Investments Noncurrent [Member] | Restricted Cash and Investments [Member] | Supranational Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cost		4,775
Gross Unrealized Gains (Losses)		3
Recorded Basis		$ 4,778

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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