Investments (Tables)

3 Months Ended

Mar. 31, 2020

Investments Debt And Equity Securities [Abstract]

Carrying Value and Amortized Cost of Company 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):

	March 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	238,541	$	1,588	$	—		$	240,129
Government sponsored enterprise securities		71,030		292		—			71,322
Corporate debt securities		112,075		74		(491	)		111,658
Commercial paper		55,204		40		(6	)		55,238
	$	476,850	$	1,994	$	(497	)	$	478,347

	December 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
U.S. Treasury notes	$	228,609	$	7	$	(13	)	$	228,603
Government sponsored enterprise securities		88,920		5		(30	)		88,895
Corporate debt securities		87,785		262		(8	)		88,039
Commercial paper		102,151		61		—			102,212
	$	507,465	$	335	$	(51	)	$	507,749

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 March 31, 2020 and December 31, 2019, 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
March 31, 2020:
Corporate debt securities	$	89,774	$	(491	)	$	—	$	—	$	89,774	$	(491	)
Commercial paper		24,806		(6	)		—		—		24,806		(6	)
Total	$	114,580	$	(497	)	$	—	$	—	$	114,580	$	(497	)
	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, 2019:
U.S. Treasury notes	$	148,397	$	(13	)	$	—	$	—	$	148,397	$	(13	)
Government sponsored enterprise securities		61,103		(30	)		—		—		61,103		(30	)
Corporate debt securities		11,334		(8	)		—		—		11,334		(8	)
Total	$	220,834	$	(51	)	$	—	$	—	$	220,834	$	(51	)