Basis of Presentation and Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) segment	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of operating segments | segment		1
Cumulative effect adjustment to accumulated deficit				$ 9,229	$ 0
Other income (expense), net	$ 53,900	$ 149,400
Deferred tax asset				1,600,000
Deferred tax assets, valuation allowance	204,700	204,700
HIV Protease Inhibitor Royalty
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue				6,900
Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment to accumulated deficit				33,349	$ (9,371)
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment to accumulated deficit	$ (24,120)	$ (24,120)
Accounting Standards Update 2014-09 | Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment to accumulated deficit			$ 8,300
Accounting Standards Update 2016-01 | Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment to accumulated deficit				$ 25,100
Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax asset			204,700
Deferred tax assets, valuation allowance			$ 204,700