Cash and Cash Equivalents, and Investments - Schedule of Available For Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 840,752
Fair Value	838,254
Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	359,101	$ 387,520
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	359,101	387,520
Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	405,836	380,686
Unrealized Gain	296	470
Unrealized Loss	(1,338)	(82)
Fair Value	404,794	381,074
Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	274,570	310,102
Unrealized Gain	247	539
Unrealized Loss	(1,703)	(158)
Fair Value	273,114	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	359,108	318,946
Unrealized Gain	149	425
Unrealized Loss	(1,338)	(78)
Fair Value	357,919	319,293
Corporate securities \| Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	256,074	295,103
Unrealized Gain	215	533
Unrealized Loss	(1,703)	(158)
Fair Value	254,586	295,478
U.S. treasury securities \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	31,729	44,251
Unrealized Gain	127	39
Unrealized Loss	0	(4)
Fair Value	31,856	44,286
Agency bonds \| Short-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	14,999	10,000
Unrealized Gain	20	6
Unrealized Loss	0	0
Fair Value	15,019	10,006
Agency bonds \| Long-term investments:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	18,496	14,999
Unrealized Gain	32	6
Unrealized Loss	0	0
Fair Value	18,528	15,005
Cash \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	198,755	241,355
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	198,755	241,355
Money market funds \| Cash and cash equivalents:
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	160,346	146,165
Unrealized Gain	0	0
Unrealized Loss	0	0
Fair Value	$ 160,346	$ 146,165

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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