Investments (Tables)

6 Months Ended

Jun. 30, 2019

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, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
Corporate debt securities	$	130,372	$	329	$	(22	)	$	130,679
Commercial paper		176,541		235		—			176,776
	$	306,913	$	564	$	(22	)	$	307,455

	December 31, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
Corporate debt securities	$	187,371	$	39	$	(344	)	$	187,066
Commercial paper		151,774		—		(78	)		151,696
	$	339,145	$	39	$	(422	)	$	338,762

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

The following table presents gross unrealized losses and fair value for those available-for-sale investment securities that were in an unrealized loss position as of June 30, 2019 and December 31, 2018, aggregated by investment category and length of time that the 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, 2019:
Corporate debt securities	$	4,000	$	(8	)	$	26,079	$	(14	)	$	30,079	$	(22	)
Total	$	4,000	$	(8	)	$	26,079	$	(14	)	$	30,079	$	(22	)

	Less Than 12 Months					12 Months or Greater					Total
	Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses
December 31, 2018:
Corporate debt securities	$	91,265	$	(130	)	$	44,637	$	(214	)	$	135,902	$	(344	)
Commercial paper		151,696		(78	)		—		—			151,696		(78	)
Total	$	242,961	$	(208	)	$	44,637	$	(214	)	$	287,598	$	(422	)