Investments and Fair Value Measurements Short-Term and Long-Term Marketable Securities (Details) - Fair Value, Measurements, Recurring - Short-term Investments $ in Thousands	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 318,008
Gross Unrealized Gains	224
Gross Unrealized Losses	(30)
Fair Value	318,202
Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	210,891
Gross Unrealized Gains	142
Gross Unrealized Losses	(27)
Fair Value	211,006
U.S. government treasury bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	70,587
Gross Unrealized Gains	65
Gross Unrealized Losses	(2)
Fair Value	70,650
U.S. government agency bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	22,085
Gross Unrealized Gains	17
Gross Unrealized Losses	(1)
Fair Value	22,101
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	14,426
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	14,426
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 19

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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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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