Cash and Marketable Securities - Summary of Available for Sale Securities (Details) $ in Thousands	Mar. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 388,154	$ 375,094
Unrealized Holding Gains	1,470	729
Unrealized Holding Losses	(227)	(30)
Aggregate Fair Value	389,397	375,793
Short-term marketable securities:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	378,476	335,231
Unrealized Holding Gains	1,430	689
Unrealized Holding Losses	(193)	(13)
Aggregate Fair Value	379,713	335,907
Short-term marketable securities: \| U.S. government treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	272,289	249,478
Unrealized Holding Gains	1,391	594
Unrealized Holding Losses	0	(2)
Aggregate Fair Value	273,680	$ 250,070
Number of securities held in unrealized holding loss position \| security		2
Aggregate Fair Value, unrealized holding loss position		$ 9,300
Short-term marketable securities: \| Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	61,920	53,396
Unrealized Holding Gains	39	94
Unrealized Holding Losses	(193)	(11)
Aggregate Fair Value	$ 61,766	$ 53,479
Number of securities held in unrealized holding loss position \| security	10	4
Aggregate Fair Value, unrealized holding loss position	$ 35,700	$ 25,900
Short-term marketable securities: \| U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		1,999
Unrealized Holding Gains		1
Unrealized Holding Losses		0
Aggregate Fair Value		2,000
Short-term marketable securities: \| Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	44,267	30,358
Unrealized Holding Gains	0	0
Unrealized Holding Losses	0	0
Aggregate Fair Value	44,267	30,358
Long-term marketable securities:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,678	39,863
Unrealized Holding Gains	40	40
Unrealized Holding Losses	(34)	(17)
Aggregate Fair Value	9,684	39,886
Long-term marketable securities: \| U.S. government treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,525	13,865
Unrealized Holding Gains	40	6
Unrealized Holding Losses	0	(2)
Aggregate Fair Value	2,565	$ 13,869
Number of securities held in unrealized holding loss position \| security		1
Aggregate Fair Value, unrealized holding loss position		$ 10,100
Long-term marketable securities: \| Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,153	25,998
Unrealized Holding Gains	0	34
Unrealized Holding Losses	(34)	(15)
Aggregate Fair Value	$ 7,119	$ 26,017
Number of securities held in unrealized holding loss position \| security	1	3
Aggregate Fair Value, unrealized holding loss position	$ 7,100	$ 17,200

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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