Investments and Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements, Recurring

The following table summarizes the Company's investments in marketable securities and fair value measurements by investment category reported as cash equivalents and short-term investments as at September 30, 2018 (in thousands):

	Carrying Amount		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value		Level 1		Level 2
Cash equivalents:
Money market funds	$	1,054	$	—	$	—		$	1,054	$	1,054	$	—
Commercial paper	22,428		—		(4		)	22,424		—		22,424
Municipal bonds	2,519		—		—			2,519		—		2,519
Total cash equivalents	$	26,001	$	—	$	(4	)	$	25,997	$	1,054	$	24,943
Short-Term Investments:
U.S. government securities	$	28,967	$	—	$	(144	)	$	28,823	$	28,823	$	—
U.S. government agency securities	14,315		—		(85		)	14,230		—		14,230
Municipal bonds	4,961				(14		)	4,947		—		4,947
Foreign government securities	5,020		—		(15		)	5,005		—		5,005
Corporate debt securities	145,074		47		(684		)	144,437		—		144,437
Commercial paper	21,076		—		(6		)	21,070		—		21,070
Certificates of deposit	1,258		—		—			1,258		—		1,258
Asset-backed securities	34,253		3		(205		)	34,051		—		34,051
Total short-term investments	$	254,924	$	50	$	(1,153	)	$	253,821	$	28,823	$	224,998
Total cash equivalents and short-term investments	$	280,925	$	50	$	(1,157	)	$	279,818	$	29,877	$	249,941

The following table summarizes the Company's investments in marketable securities and fair value measurements by investment category reported as cash equivalents and short-term investments as at December 31, 2017 (in thousands):

	Carrying Amount		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value		Level 1		Level 2
Cash equivalents:
Money market funds	$	58,953	$	—	$	—		$	58,953	$	58,953	$	—
Commercial paper	21,930		—		(3		)	21,927		—		21,927
Total cash equivalents	$	80,883	$	—	$	(3	)	$	80,880	$	58,953	$	21,927
Short-Term Investments:
U.S. government securities	$	17,472	$	—	$	(41	)	$	17,431	$	17,431	$	—
U.S. government agency securities	11,540		—		(30		)	11,510		—		11,510
Municipal bonds	6,974		2		(8		)	6,968		—		6,968
Foreign government securities	7,499		—		(27		)	7,472		—		7,472
Corporate debt securities	105,144		3		(273		)	104,874		—		104,874
Commercial paper	30,798		1		(9		)	30,790		—		30,790
Certificates of deposit	1,255		—		—			1,255		—		1,255
Asset-backed securities	15,310		—		(76		)	15,234		—		15,234
Total short-term investments	$	195,992	$	6	$	(464	)	$	195,534	$	17,431	$	178,103
Total cash equivalents and short-term investments	$	276,875	$	6	$	(467	)	$	276,414	$	76,384	$	200,030

Investments Classified by Contractual Maturity Date

The following table summarizes the estimated amortized cost and fair value of the Company's marketable securities by the contractual maturity date as at September 30, 2018 (in thousands):

	Amortized Cost		Fair Value
Due less than one year	$	193,309	$	192,753
Due in one to five years	87,616		87,065
Total	$	280,925	$	279,818

The following table summarizes the estimated amortized costs and fair value of the Company's marketable securities by the contractual maturity date as at December 31, 2017 (in thousands):

	Amortized Costs		Fair Value
Due less than one year	$	157,651	$	157,573
Due in one to five years	119,224		118,841
Total	$	276,875	$	276,414