Fair Value Measurement (Tables)

9 Months Ended

Sep. 30, 2018

Summary of Investments Measured at Fair Value on Recurring Basis

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

	September 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	$	61	$	—		$	61	$	121	$	—		$	121
U.S. treasuries		—		—			—		100		—			100
Total cash equivalents		61		—			61		221		—			221
Investments:
U.S. treasuries		346		(1	)		345		199		—			199
Corporate bonds		45		—			45		400		—			400
U.S. government agency securities		5		—			5		65		—			65
Municipal bonds		—		—			—		10		—			10
Total current investments		396		(1	)		395		674		—			674
Long term:
Investments:
U.S. treasuries		745		(10	)		735		202		(2	)		200
Mortgage backed securities		501		(18	)		483		577		(5	)		572
Corporate bonds		383		(11	)		372		419		(2	)		417
U.S. government agency securities		50		(1	)		49		—		—			—
Asset backed securities		10		—			10		10		—			10
Total long term investments		1,689		(40	)		1,649		1,208		(9	)		1,199
Restricted cash and investments ⁽¹⁾:
Corporate bonds		187,203		(4,673	)		182,530		184,808		(953	)		183,855
Mortgage backed securities		93,211		(3,178	)		90,033		86,240		(595	)		85,645
U.S. treasuries		54,296		(492	)		53,804		45,833		(143	)		45,690
U.S. government agency securities		45,570		(1,785	)		43,785		38,168		(222	)		37,946
Supranational bonds		4,764		(67	)		4,697		—		—			—
Money market funds		416		—			416		16,018		—			16,018
Municipal bonds		80		—			80		472		(14	)		458
Asset backed securities		75		(1	)		74		—		—			—
Commercial paper		—		—			—		18,973		—			18,973
Total restricted cash and investments		385,615		(10,196	)		375,419		390,512		(1,927	)		388,585
Total investments	$	387,761	$	(10,237	)	$	377,524	$	392,615	$	(1,936	)	$	390,679

(1) Included in restricted cash and investments within the condensed consolidated balance sheet as of September 30, 2018 is restricted cash of $70.0 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 September 30, 2018 and December 31, 2017 measured at fair value on a recurring basis by fair value hierarchy level (in thousands):

	September 30, 2018						December 31, 2017
	Total						Total
	Recorded						Recorded
	Basis		Level 2		Other ⁽¹⁾		Basis		Level 2		Other ⁽¹⁾
Cash equivalents:
Money market funds	$	61	$	—	$	61	$	121	$	—	$	121
U.S. treasuries		—		—		—		100		100		—
Investments:
U.S. treasuries		1,080		1,080		—		399		399		—
Mortgage backed securities		483		483		—		572		572		—
Corporate bonds		417		417		—		817		817		—
U.S. government agency securities		54		54		—		65		65		—
Asset backed securities		10		10		—		10		10		—
Municipal bonds		—		—		—		10		10		—
Restricted cash and investments:
Corporate bonds		182,530		182,530		—		183,855		183,855		—
Mortgage backed securities		90,033		90,033		—		85,645		85,645		—
U.S. treasuries		53,804		53,804		—		45,690		45,690		—
U.S. government agency securities		43,785		43,785		—		37,946		37,946		—
Supranational bonds		4,697		4,697		—		—		—		—
Money market funds		416		—		416		16,018		—		16,018
Municipal bonds		80		80		—		458		458		—
Asset backed securities		74		74		—		—		—		—
Commercial paper		—		—		—		18,973		18,973		—
Total investments	$	377,524	$	377,047	$	477	$	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.