Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Aug. 08, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Aug. 14, 2017	Dec. 31, 2016	Dec. 31, 2015
Policies
Common stock, shares issued		53,708,000		53,708,000			52,665,000
Net (loss) income		$ (27,119)	$ (26,017)	$ (90,812)	$ (57,858)
Accumulated deficit		436,660		436,660			$ 345,848
Cash and cash equivalents		11,211	$ 25,322	11,211	$ 25,322		15,256	$ 28,947
Marketable securities		135,017		135,017			130,860
Short-term Credit Line, outstanding balance		50,097		50,097			49,624
Long-term Term Loan, carrying amount		73,202		73,202
Restricted cash
Restricted cash, current portion		45		45			1,092
Restricted cash, long term portion		$ 342		$ 342			$ 342
2017 Term Loan
Policies
Maximum borrowing capacity	$ 100,000
Available borrowing capacity	75,000
Remaining borrowing capacity	$ 25,000
Debt instrument, term	84 months
Common stock, shares issued						300,000
2017 Term Loan | Base Rate
Policies
Spread on interest rate (as a percent)	8.75%
Base interest rate (as a percent)	1.00%