Debt - Deerfield Facility Agreement (Details) - USD ($)				1 Months Ended	12 Months Ended
	Sep. 01, 2016	Nov. 21, 2014	Mar. 20, 2014	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 22, 2017	Feb. 05, 2016	Feb. 04, 2016	Mar. 17, 2014
Line of Credit Facility [Line Items]
Exercise price of warrants (dollars per share)							$ 2.00
Conversion of preferred stock into common stock, shares				268,614
Repayments under lines of credit					$ 98,443,000	$ 134,792,000
Loss on debt extinguishment						$ (9,478,000)
Deerfield
Line of Credit Facility [Line Items]
Maximum borrowing capacity										$ 50,000,000
Line of credit		$ 6,000,000	$ 20,000,000
Net proceeds from initial draw under Facility Agreement		$ 5,900,000	$ 19,500,000
Debt instrument, stated interest rate									8.75%
Conversion of preferred stock into common stock, shares				268,614
Conversion of preferred stock into common stock				$ 1,100,000
Repayments under lines of credit	$ 33,500,000
Repayments of lines of credit, principle and accrued interest	27,900,000
Repayments of lines of credit, prepayment of premium	5,600,000
Write off of unamortized expense	3,900,000
Loss on debt extinguishment	$ (9,500,000)
Deerfield | Initial warrants
Line of Credit Facility [Line Items]
Number of warrants issued (in shares)										520,833
Exercise price of warrants (dollars per share)										$ 16.68
Deerfield | Draw warrants
Line of Credit Facility [Line Items]
Maximum borrowing capacity										$ 50,000,000
Deerfield | Draw warrants | Maximum
Line of Credit Facility [Line Items]
Number of securities called by warrants associated with each disbursement borrowing (in shares)										833,333
Second amendment with Deerfield
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate								14.75%