Cash and Cash Equivalents, and Investments - Schedule of Available For Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 1,752,190
Fair Value	1,754,783
Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	527,541	$ 387,520
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	527,541	387,520
Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	720,726	380,686
Unrealized Gain	2,682	470
Unrealized Loss	(81)	(82)
Fair Value	723,327	381,074
Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	521,269	310,102
Unrealized Gain	627	539
Unrealized Loss	(635)	(158)
Fair Value	521,261	310,483
Commercial paper \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	204,044	7,489
Unrealized Gain	38	0
Unrealized Loss	(24)	0
Fair Value	204,058	7,489
Corporate securities \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	516,682	318,946
Unrealized Gain	2,644	425
Unrealized Loss	(57)	(78)
Fair Value	519,269	319,293
Corporate securities \| Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	456,774	295,103
Unrealized Gain	602	533
Unrealized Loss	(635)	(158)
Fair Value	456,741	295,478
U.S. treasury securities \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost		44,251
Unrealized Gain		39
Unrealized Loss		(4)
Fair Value		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	64,495	14,999
Unrealized Gain	25	6
Unrealized Loss	0	0
Fair Value	64,520	15,005
Cash \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	17,346	241,355
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	17,346	241,355
Money market funds \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	202,522	146,165
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	202,522	$ 146,165
U.S. treasury securities \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	307,673
Unrealized Gain	0
Unrealized Loss	0
Fair Value	$ 307,673

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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