Collaboration Agreements (Teva Agreement) (Details) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended				12 Months Ended
	Jan. 01, 2018	Sep. 30, 2016	Sep. 30, 2016	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Prepaid expenses and other current assets				$ 155,451	$ 224,972
Teva Pharmaceuticals [Member] | Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Up-front payment received		$ 250,000	$ 250,000
Revenue Recognition, Milestone Method, Revenue Recognized					35,000	$ 25,000
Collaboration revenue				58,600			$ 33,100
Teva Pharmaceuticals [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Prepaid expenses and other current assets				40,625	71,297
Deferred Revenue				686,000
Deferred Revenue				227,714	$ 197,357
Accounting Standards Update 2014-09 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred Revenue, Period Increase (Decrease)	$ 143,400
Accounting Standards Update 2014-09 [Member] | Teva Pharmaceuticals [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred Revenue, Period Increase (Decrease)				48,216
Deferred Revenue, Revenue Recognized				$ (18,917)
Scenario, Forecast [Member] | Teva Pharmaceuticals [Member] | Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative Arrangement, Additional Eligible Aggregate Payments								$ 1,890,000
Scenario, Forecast [Member] | Teva Pharmaceuticals [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate future development milestone payments the Company is eligible to receive								$ 400,000