Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2018

Summary of Investments Measured at Fair Value on Recurring Basis

The following table summarizes the Company’s investments at December 31, 2018 and 2017 measured at fair value on a recurring basis (in thousands):

	December 31, 2018							December 31, 2017
										Gross
			Gross							Unrealized
			Unrealized			Recorded				Gains			Recorded
	Cost		(Losses)			Basis		Cost		(Losses)			Basis
Current:
Cash equivalents:
Money market funds	$	30	$	—		$	30	$	121	$	—		$	121
U.S. treasuries		—		—			—		100		—			100
Total cash equivalents		30		—			30		221		—			221
Investments:
U.S. treasuries		347		—			347		199		—			199
U.S. government agency securities		50		(1	)		49		65		—			65
Corporate bonds		20		—			20		400		—			400
Municipal bonds		—		—			—		10		—			10
Certificates of deposit		—		—			—		—		—			—
Total current investments		417		(1	)		416		674		—			674
Long term:
Investments:
U.S. treasuries		794		(3	)		791		202		(2	)		200
Mortgage backed securities		484		(13	)		471		577		(5	)		572
Corporate bonds		422		(7	)		415		419		(2	)		417
Asset backed securities		10		—			10		10		—			10
Total long term investments		1,710		(23	)		1,687		1,208		(9	)		1,199
Restricted cash and investments ⁽¹⁾:
Corporate bonds		185,116		(3,739	)		181,377		184,808		(953	)		183,855
Mortgage backed securities		89,426		(2,026	)		87,400		86,240		(595	)		85,645
U.S. government agency securities		45,548		(908	)		44,640		38,168		(222	)		37,946
U.S. treasuries		44,304		(283	)		44,021		45,833		(143	)		45,690
Supranational		4,765		(24	)		4,741		—		—			—
Mutual funds		1,093		—			1,093		—		—			—
Money market funds		419		—			419		16,018		—			16,018
Asset backed securities		75		(1	)		74		—		—			—
Municipal bonds		50		—			50		472		(14	)		458
Commercial paper		—		—			—		18,973		—			18,973
Total restricted cash and investments		370,796		(6,981	)		363,815		390,512		(1,927	)		388,585
Total investments	$	372,953	$	(7,005	)	$	365,948	$	392,615	$	(1,936	)	$	390,679

(1) Included in restricted cash and investments within the consolidated balance sheets as of December 31, 2018 and 2017 is restricted cash of $104.5 million and $6.3 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, 2018 and 2017 measured at fair value on a recurring basis by fair value hierarchy level (in thousands):

	December 31, 2018										December 31, 2017
	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	$	30	$	—	$	—	$	—	$	30	$	121	$	—	$	—	$	—	$	121
U.S. treasuries		—		—		—		—		—		100		—		100		—
Investments:
U.S. treasuries		1,138		—		1,138		—		—		399		—		399		—		—
Mortgage backed securities		471		—		471		—		—		572		—		572		—		—
Corporate bonds		435		—		435		—		—		817		—		817		—		—
U.S. government agency securities		49		—		49		—		—		65		—		65		—		—
Asset backed securities		10		—		10		—		—		10		—		10		—		—
Municipal bonds		—		—		—		—		—		10		—		10		—		—
Restricted cash and investments:
Corporate bonds		181,377		—		181,377		—		—		183,855		—		183,855		—		—
Mortgage backed securities		87,400		—		87,400		—		—		85,645		—		85,645		—		—
U.S. government agency securities		44,640		—		44,640		—		—		37,946		—		37,946		—		—
U.S. treasuries		44,021		—		44,021		—		—		45,690		—		45,690		—		—
Supranational		4,741		—		4,741		—		—		—		—		—		—		—
Mutual funds		1,093		1,093		—		—		—		—		—		—		—		—
Money market funds		419		—		—		—		419		16,018		—		—		—		16,018
Asset backed securities		74		—		74		—		—		—		—		—		—		—
Municipal bonds		50		—		50		—		—		458		—		458		—		—
Commercial paper		—		—		—		—		—		18,973		—		18,973		—		—
Total investments	$	365,948	$	1,093	$	364,406	$	—	$	449	$	390,679	$	—	$	374,540	$	—	$	16,139

(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, 2018 and 2017. Actual maturities may differ from contractual maturities because borrowers may have the right to prepay obligations with our without prepayment penalties.

	December 31, 2018
(In thousands)	Less than 1 Year		Between 1 to 5 Years		Between 5 to 10 Years		After 10 Years		Total
Corporate bonds	$	14,183	$	144,894	$	22,735	$	—	$	181,812
U.S. treasuries		4,919		40,240		—		—		45,159
U.S. government agency securities		4,788		7,031		32,870		—		44,689
Supranational		—		4,741		—		—		4,741
Money market funds		449		—		—		—		449
Asset backed securities		—		84		—		—		84
Municipal bonds		50		—		—		—		50
Total	$	24,389	$	196,990	$	55,605	$	—	$	276,984

	December 31, 2017
(In thousands)	Less than 1 Year		Between 1 to 5 Years		Between 5 to 10 Years		After 10 Years		Total
Corporate bonds	$	5,426	$	153,567	$	19,102	$	6,577	$	184,672
U.S. treasuries		32,466		13,723		—		—		46,189
U.S. government agency securities		65		4,355		33,591		—		38,011
Commercial Paper		18,973		—		—		—		18,973
Money market funds		16,139		—		—		—		16,139
Municipal bonds		468		—		—		—		468
Asset backed securities		—		10		—		—		10
Total	$	73,537	$	171,655	$	52,693	$	6,577	$	304,462