Fair Value Measurement (Tables)

6 Months Ended

Jun. 30, 2018

Summary of Investments Measured at Fair Value on Recurring Basis

The following table summarizes the Company’s investments at June 30, 2018 and December 31, 2017 measured at fair value on a recurring basis (in thousands):

	June 30, 2018							December 31, 2017
			Gross							Gross
			Unrealized							Unrealized
			Gains			Recorded				Gains			Recorded
	Cost		(Losses)			Basis		Cost		(Losses)			Basis
Current:
Cash equivalents:
Money market funds	$	56	$	—		$	56	$	121	$	—		$	121
U.S. treasuries		—		—			—		100		—			100
Total cash equivalents		56		—			56		221		—			221
Investments:
U.S. treasuries		344		—			344		199		—			199
Corporate bonds		61		(1	)		60		400		—			400
U.S. government agency securities		60		—			60		65		—			65
Municipal bonds		—		—			—		10		—			10
Total current investments		465		(1	)		464		674		—			674
Long term:
Investments:
U.S. treasuries		645		(7	)		638		202		(2	)		200
Mortgage backed securities		522		(14	)		508		577		(5	)		572
Corporate bonds		384		(11	)		373		419		(2	)		417
U.S. government agency securities		49		—			49		—		—			—
Asset backed securities		10		—			10		10		—			10
Total long term investments		1,610		(32	)		1,578		1,208		(9	)		1,199
Restricted cash and investments ⁽¹⁾:
Corporate bonds		190,230		(4,512	)		185,718		184,808		(953	)		183,855
Mortgage backed securities		97,337		(2,610	)		94,727		86,240		(595	)		85,645
U.S. treasuries		72,776		(365	)		72,411		45,833		(143	)		45,690
U.S. government agency securities		45,592		(1,233	)		44,359		38,168		(222	)		37,946
Supranational bonds		4,763		(49	)		4,714		—		—			—
Money market funds		361		—			361		16,018		—			16,018
Municipal bonds		185		—			185		472		(14	)		458
Asset backed securities		75		(1	)		74		—		—			—
Commercial paper		—		—			—		18,973		—			18,973
Total restricted cash and investments		411,319		(8,770	)		402,549		390,512		(1,927	)		388,585
Total investments	$	413,450	$	(8,803	)	$	404,647	$	392,615	$	(1,936	)	$	390,679

(1) Included in restricted cash and investments within the condensed consolidated balance sheet as of June 30, 2018 is restricted cash and long term workers' compensation deposits of $20.5 million, 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 June 30, 2018 and December 31, 2017 measured at fair value on a recurring basis by fair value hierarchy level (in thousands):

	June 30, 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	$	56	$	—	$	—	$	—	$	56	$	121	$	—	$	—	$	—	$	121
U.S. treasuries		—		—		—		—		—		100		—		100		—		—
Investments:
U.S. treasuries		982		—		982		—		—		399		—		399		—		—
Mortgage backed securities		508		—		508		—		—		572		—		572		—		—
Corporate bonds		433		—		433		—		—		817		—		817		—		—
U.S. government agency securities		109		—		109		—		—		65		—		65		—		—
Asset backed securities		10		—		10		—		—		10		—		10		—		—
Municipal bonds		—		—		—		—		—		10		—		10		—		—
Restricted cash and investments:
Corporate bonds		185,718		—		185,718		—		—		183,855		—		183,855		—		—
Mortgage backed securities		94,727		—		94,727		—		—		85,645		—		85,645		—		—
U.S. treasuries		72,411		—		72,411		—		—		45,690		—		45,690		—		—
U.S. government agency securities		44,359		—		44,359		—		—		37,946		—		37,946		—		—
Supranational bonds		4,714		—		4,714		—		—		—		—		—		—		—
Money market funds		361		—		—		—		361		16,018		—		—		—		16,018
Municipal bonds		185		—		185		—		—		458		—		458		—		—
Asset backed securities		74		—		74		—		—		—		—		—		—		—
Commercial paper		—		—		—		—		—		18,973		—		18,973		—		—
Total investments	$	404,647	$	—	$	404,230	$	—	$	417	$	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.