Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Aug. 08, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Policies
Common stock, shares issued		53,208,000		53,208,000		52,665,000
Net (loss) income		$ (27,732)	$ (23,156)	$ (63,693)	$ (31,841)
Accumulated deficit		409,541		409,541		$ 345,848
Cash and cash equivalents		7,138	$ 16,557	7,138	$ 16,557	15,256	$ 28,947
Short-term investments		94,988		94,988		130,860
Outstanding debt with accrued interest		50,022		50,022		49,624
Restricted cash
Restricted cash, current portion		764		764		1,092
Restricted cash, long term portion		$ 342		$ 342		$ 342
2017 Term Loan | Subsequent Event
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 | Subsequent Event
Policies
Spread on interest rate (as a percent)	8.75%
Base interest rate (as a percent)	1.00%