Investments (Tables)

6 Months Ended

Jun. 30, 2018

Investments Debt And Equity Securities [Abstract]

Carrying Value and Amortized Cost of Company’s Investments Summarized by Major Security Type

The carrying value and amortized cost of the Company’s investments, summarized by major security type, consisted of the following (in thousands):

	June 30, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	—	$	—	$	—		$	—
Government sponsored enterprise securities		—		—		—			—
Corporate debt securities		139,304		—		(502	)		138,802
Commercial paper		43,879		6		(14	)		43,871
Equity securities		3,149		—		(247	)		2,902
	$	186,332	$	6	$	(763	)	$	185,575

	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	32,976	$	—	$	(12	)	$	32,964
Government sponsored enterprise securities		10,082		—		(10	)		10,072
Corporate debt securities		138,650		1		(321	)		138,330
Commercial paper		90,623		—		(65	)		90,558
	$	272,331	$	1	$	(408	)	$	271,924

Summary of Gross Unrealized Losses and Fair Value of Available-For-Sale Investments in Unrealized Loss Position

The following table presents gross unrealized losses and fair value for those available-for-sale investments that were in an unrealized loss position as of June 30, 2018 and December 31, 2017, aggregated by investment category and length of time that individual securities have been in a continuous loss position (in thousands):

	Less Than 12 Months					12 Months or Greater				Total
	Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
June 30, 2018:
U.S. Treasury notes	$	—	$	—		$	—	$	—	$	—	$	—
Government sponsored enterprise securities		—		—			—		—		—		—
Corporate debt securities		136,308		(502	)		—		—		136,308		(502	)
Commercial paper		24,061		(14	)		—		—		24,061		(14	)
Total	$	160,369	$	(516	)	$	—	$	—	$	160,369	$	(516	)
December 31, 2017:
U.S. Treasury notes	$	32,964	$	(12	)	$	—	$	—		32,964		(12	)
Government sponsored enterprise securities		10,072		(10	)		—		—		10,072		(10	)
Corporate debt securities		129,820		(321	)		—		—		129,820		(321	)
Commercial paper		90,558		(65	)		—		—		90,558		(65	)
Total	$	263,414	$	(408	)	$	—	$	—	$	263,414	$	(408	)