Cash and Cash Equivalents, and Investments - Schedule of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	$ 1,652,188
Fair Value	1,653,994
Cash and cash equivalents:
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	479,853	$ 387,520
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	479,853	387,520
Short-term investments:
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	664,119	380,686
Unrealized Gain	1,502	470
Unrealized Loss	(54)	(82)
Fair Value	665,567	381,074
Long-term investments
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	523,270	310,102
Unrealized Gain	641	539
Unrealized Loss	(283)	(158)
Fair Value	523,628	310,483
Cash \| Cash and cash equivalents:
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	15,054	241,355
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	15,054	241,355
Money market funds \| Cash and cash equivalents:
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	464,799	146,165
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	464,799	146,165
Commercial paper \| Short-term investments:
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	204,152	7,489
Unrealized Gain	24	0
Unrealized Loss	(6)	0
Fair Value	204,170	7,489
Corporate debt securities \| Short-term investments:
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	459,967	318,946
Unrealized Gain	1,478	425
Unrealized Loss	(48)	(78)
Fair Value	461,397	319,293
Corporate debt securities \| Long-term investments
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	484,275	295,103
Unrealized Gain	605	533
Unrealized Loss	(283)	(158)
Fair Value	484,597	295,478
Agency Securities \| Short-term investments:
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost		10,000
Unrealized Gain		6
Unrealized Loss		0
Fair Value		10,006
Agency Securities \| Long-term investments
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	38,995	14,999
Unrealized Gain	36	6
Unrealized Loss	0	0
Fair Value	$ 39,031	15,005
U.S. treasury securities \| Short-term investments:
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost		44,251
Unrealized Gain		39
Unrealized Loss		(4)
Fair Value		$ 44,286

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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