Organization and Basis of Presentation - Prior Period Errors (Details) - USD ($) $ in Thousands	3 Months Ended							6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Research and Development Expense	$ 19,475					$ 16,046		$ 39,856	$ 29,396
Accrued Liabilities and Other Liabilities	10,404		$ 12,857	[1]				10,404
Effect of Change
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accrued Liabilities and Other Liabilities	$ (270)							$ (270)
Overstatement due to clinical trial accrual errors | Effect of Change
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Research and Development Expense		$ 500	1,400		$ 1,100	$ 900	$ 200
Accrued Liabilities and Other Liabilities			$ 3,600

[1] Derived from the audited consolidated financial statements included in the Company’s Annual Report on Form 10K for the year ended December 31, 2018.