Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2021

Summary of Investments Measured at Fair Value on Recurring Basis

The following table summarizes the Company’s investments at December 31, 2021 and 2020 measured at fair value on a recurring basis (in thousands):

	December 31, 2021							December 31, 2020
			Gross							Gross
			Unrealized							Unrealized
			Gains			Recorded				Gains			Recorded
	Cost		(Losses)			Basis		Cost		(Losses)			Basis
Current:
Cash equivalents:
Money market funds	$	13,384	$	—		$	13,384	$	42,007	$	—		$	42,007
Total cash equivalents		13,384		—			13,384		42,007		—			42,007
Investments:
Corporate bonds		41,954		(136	)		41,818		50,918		884			51,802
Asset backed securities		29,533		(38	)		29,495		36,948		(146	)		36,802
U.S. government agency securities		7,383		418			7,801		7,396		752			8,148
Mortgage backed securities		18,089		(440	)		17,649		4,367		24			4,391
U.S. treasuries		—		—			—		100		1			101
Total current investments		96,959		(196	)		96,763		99,729		1,515			101,244
Restricted cash and investments ⁽¹⁾:
Corporate bonds		117,700		(17	)		117,683		88,902		4,091			92,993
Mortgage backed securities		64,217		764			64,981		48,795		2,356			51,151
Money market funds		528		—			528		40,063		(4	)		40,059
U.S. government agency securities		32,898		1,281			34,179		29,737		2,466			32,203
Mutual funds		6,273		—			6,273		5,036		—			5,036
Supranational bonds		—		—			—		4,775		3			4,778
U.S. treasuries		67,614		(342	)		67,272		4,371		19			4,390
Asset backed securities		107		1			108		256		4			260
Total restricted cash and investments		289,337		1,687			291,024		221,935		8,935			230,870
Total investments	$	399,680	$	1,491		$	401,171	$	363,671	$	10,450		$	374,121

(1) Included in restricted cash and investments within the consolidated balance sheets as of December 31, 2021 and 2020 is restricted cash of $9.2 million and $124.3 million, respectively, which is excluded from the table above. Restricted cash and investments are classified as current and noncurrent on the balance sheet based on the nature of the restriction.

Summary of Assets Measured at Fair Value on Recurring Basis

The following table summarizes the Company's investments at December 31, 2021 and 2020 measured at fair value on a recurring basis by fair value hierarchy level (in thousands):

	December 31, 2021										December 31, 2020
	Total										Total
	Recorded										Recorded
	Basis		Level 1		Level 2		Level 3		Other ⁽¹⁾		Basis		Level 1		Level 2		Level 3		Other ⁽¹⁾
Cash equivalents:
Money market funds		13,384	$	—	$	—	$	—	$	13,384	$	42,007	$	—	$	—	$	—	$	42,007
Investments:
Corporate bonds		41,818		—		41,818		—		—		51,802		—		51,802		—		—
Asset backed securities		29,495		—		29,495		—		—		36,802		—		36,802		—		—
U.S. government agency securities		7,801		—		7,801		—		—		8,148		—		8,148		—		—
Mortgage backed securities		17,649		—		17,649		—		—		4,391		—		4,391		—		—
U.S. treasuries		—		—		—		—		—		101		—		101		—		—
Restricted cash and investments:
Corporate bonds		117,683		—		117,683		—		—		92,993		—		92,993		—		—
Mortgage backed securities		64,981		—		64,981		—		—		51,151		—		51,151		—		—
Money market funds		528		—		—		—		528		40,059		—		—		—		40,059
U.S. government agency securities		34,179		—		34,179		—		—		32,203		—		32,203		—		—
Mutual funds		6,273		6,273		—		—		—		5,036		5,036		—		—		—
Supranational bonds		—		—		—		—		—		4,778		—		4,778		—		—
U.S. treasuries		67,272		—		67,272		—		—		4,390		—		4,390		—		—
Asset backed securities		108		—		108		—		—		260		—		260		—		—
Total investments	$	401,171	$	6,273	$	380,986	$	—	$	13,912	$	374,121	$	5,036	$	287,019	$	—	$	82,066

(1) Investments in money market funds measured at fair value using the net asset value per share practical expedient are not subject to hierarchy level classification disclosure. The Company invests in money market funds that seek to maintain a stable net asset value. These investments include commingled funds that comprise high-quality short-term securities representing liquid debt and monetary instruments where the redemption value is likely to be the fair value. Redemption is permitted daily without written notice.

Summary of Contractual Maturities of Available for Sale Securities

The following table summarizes the contractual maturities of the Company’s available for sale securities at December 31, 2021 and 2020. Actual maturities may differ from contractual maturities because borrowers may have the right to prepay obligations with or without prepayment penalties.

	December 31, 2021
(In thousands)	Less than 1 Year		Between 1 to 5 Years		Between 5 to 10 Years		After 10 Years		Total
Corporate bonds	$	24,601	$	35,570	$	99,180	$	150	$	159,501
Money market funds		13,657		—		—		—		13,657
U.S. government agency securities		—		25,171		16,809		—		41,980
Asset backed securities		—		108		2,200		27,295		29,603
Supranational bonds		—		—		—		—		—
U.S. treasuries		953		4,295		62,024		—		67,272
Total	$	39,211	$	65,144	$	180,213	$	27,445	$	312,013

	December 31, 2020
(In thousands)	Less than 1 Year		Between 1 to 5 Years		Between 5 to 10 Years		After 10 Years		Total
Corporate bonds	$	49,308	$	61,315	$	34,172	$	—	$	144,795
Money market funds		82,066		—		—		—		82,066
U.S. government agency securities		1,013		18,668		20,670		—		40,351
Asset backed securities		2		267		—		36,793		37,062
Supranational bonds		4,778		—		—		—		4,778
U.S. treasuries		1,367		1,504		1,620		—		4,491
Total	$	138,534	$	81,754	$	56,462	$	36,793	$	313,543