Cash and Marketable Securities - Summary of Available for Sale Securities (Details) $ in Thousands	Jun. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 418,668	$ 375,094
Unrealized Holding Gains	958	729
Unrealized Holding Losses	0	(30)
Aggregate Fair Value	419,626	375,793
Short-term marketable securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	411,541	335,231
Unrealized Holding Gains	856	689
Unrealized Holding Losses	0	(13)
Aggregate Fair Value	412,397	335,907
Short-term marketable securities \| U.S. government treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	332,659	249,478
Unrealized Holding Gains	553	594
Unrealized Holding Losses	0	(2)
Aggregate Fair Value	$ 333,212	$ 250,070
Number of securities held in unrealized holding loss position \| security	4	2
Aggregate fair value, unrealized holding loss position		$ 9,300
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 \| Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 49,458	53,396
Unrealized Holding Gains	303	94
Unrealized Holding Losses	0	(11)
Aggregate Fair Value	49,761	$ 53,479
Number of securities held in unrealized holding loss position \| security		4
Aggregate fair value, unrealized holding loss position		$ 25,900
Short-term marketable securities \| Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	29,424	30,358
Unrealized Holding Gains	0	0
Unrealized Holding Losses	0	0
Aggregate Fair Value	29,424	30,358
Long-term marketable securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,127	39,863
Unrealized Holding Gains	102	40
Unrealized Holding Losses	0	(17)
Aggregate Fair Value	7,229	39,886
Long-term marketable securities \| U.S. government treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		13,865
Unrealized Holding Gains		6
Unrealized Holding Losses		(2)
Aggregate Fair Value		$ 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	7,127	25,998
Unrealized Holding Gains	102	34
Unrealized Holding Losses	0	(15)
Aggregate Fair Value	$ 7,229	$ 26,017
Number of securities held in unrealized holding loss position \| security		3
Aggregate fair value, unrealized holding loss position		$ 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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