Cash and Cash Equivalents, and Investments - Schedule of Available For Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 961,191
Fair Value	965,426
Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	285,064	$ 387,520
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	285,064	387,520
Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	414,936	380,686
Unrealized Gain	2,635	470
Unrealized Loss	(41)	(82)
Fair Value	417,530	381,074
Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	278,851	310,102
Unrealized Gain	1,860	539
Unrealized Loss	(219)	(158)
Fair Value	280,492	310,483
Commercial paper \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost		7,489
Unrealized Gain		0
Unrealized Loss		0
Fair Value		7,489
Corporate securities \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	399,894	318,946
Unrealized Gain	2,581	425
Unrealized Loss	(41)	(78)
Fair Value	402,434	319,293
Corporate securities \| Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	218,099	295,103
Unrealized Gain	1,851	533
Unrealized Loss	(214)	(158)
Fair Value	219,736	295,478
U.S. treasury securities \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	15,042	44,251
Unrealized Gain	54	39
Unrealized Loss	0	(4)
Fair Value	15,096	44,286
Agency bonds \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost		10,000
Unrealized Gain		6
Unrealized Loss		0
Fair Value		10,006
Agency bonds \| Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	60,752	14,999
Unrealized Gain	9	6
Unrealized Loss	(5)	0
Fair Value	60,756	15,005
Cash \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	17,660	241,355
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	17,660	241,355
Money market funds \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	150,002	146,165
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	150,002	$ 146,165
U.S. treasury securities \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	117,402
Unrealized Gain	0
Unrealized Loss	0
Fair Value	$ 117,402

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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