Financial Instruments - Summary of Cash and Available-for-Sale Securities by Significant Investment Category (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,024,106	$ 1,037,372
Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,259,980	1,695,737
Unrealized Gains	3,047	120
Unrealized Losses	(40)	(1,440)
Fair Value	1,262,987	1,694,417
Level 2 \| Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Fair Value	235,876	658,364
Level 2 \| Current Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	867,124	863,063
Level 2 \| Non- Current Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	159,987	172,990
Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	225,874	658,365
Unrealized Gains	0	20
Unrealized Losses	0	(21)
Fair Value	225,874	658,364
Cash and Cash Equivalents \| Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Fair Value	225,874	658,364
Cash and Cash Equivalents \| Current Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	0
Cash and Cash Equivalents \| Non- Current Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	0
Certificates of deposit \| Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	82,028	173,102
Unrealized Gains	79	42
Unrealized Losses	(6)	(36)
Fair Value	82,101	173,108
Certificates of deposit \| Level 2 \| Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Fair Value	10,002	0
Certificates of deposit \| Level 2 \| Current Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	69,197	157,920
Certificates of deposit \| Level 2 \| Non- Current Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	2,902	15,188
U.S. treasury securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	117,891	152,205
Unrealized Gains	260	18
Unrealized Losses	(2)	(48)
Fair Value	118,149	152,175
U.S. treasury securities \| Level 2 \| Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	0
U.S. treasury securities \| Level 2 \| Current Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	110,186	152,175
U.S. treasury securities \| Level 2 \| Non- Current Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	7,963	0
Debt securities of U.S. government agencies and corporate entities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	834,187	712,065
Unrealized Gains	2,708	40
Unrealized Losses	(32)	(1,335)
Fair Value	836,863	710,770
Debt securities of U.S. government agencies and corporate entities \| Level 2 \| Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	0
Debt securities of U.S. government agencies and corporate entities \| Level 2 \| Current Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	687,741	552,968
Debt securities of U.S. government agencies and corporate entities \| Level 2 \| Non- Current Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 149,122	$ 157,802

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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Amount, before tax, of unrealized loss 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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Amortized cost of 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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Amount of 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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