Debt - Senior Convertible Notes (Details) - USD ($)				1 Months Ended		3 Months Ended								12 Months Ended
	Feb. 28, 2017	Mar. 18, 2016	Nov. 03, 2014	Mar. 31, 2017	Nov. 30, 2016	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 01, 2014
Debt Instrument [Line Items]
Net proceeds from offering														$ 95,140,000	$ 0	$ 0
Interest payable on senior convertible notes						$ 233,000				$ 294,000				233,000	294,000
Debt conversion amount														4,912,000	137,941,000	40,989,000
Common stock issued for interest on Notes															2,445,000	0
Amortization of deferred debt costs and debt discount														1,342,000	6,921,000	4,566,000
Debt conversion expense						0	$ 0	$ 0	$ 1,209,000	14,543,000	$ 0	$ 0	$ 25,615,000	$ 1,209,000	$ 40,158,000	0
Payment for indenture consent	$ 1,600,000
Common Shares
Debt Instrument [Line Items]
Debt conversion per original conversion price (in shares)		9,600,000												212,800	12,161,671
Convertible Senior Notes Due 2019
Debt Instrument [Line Items]
Aggregate principal amount			$ 200,000,000			18,603,000				23,500,000.0				$ 18,603,000	$ 23,500,000.0	159,000,000
Interest rate			7.50%
Additional aggregate principal amount pertaining to the over-allotment option granted			$ 25,000,000
Net proceeds from offering			$ 187,300,000
Additional interest expense from acceleration of deferred debt costs					$ 2,000,000									1,300,000	6,700,000	12,900,000
Interest payable on senior convertible notes										300,000					300,000
Conversion rate (per $1,000 principal amount of notes)		0.3215434
Conversion price (in dollars per share)		$ 3.11	$ 3.11
Long-term debt, gross						$ 18,603,000				$ 23,514,000				18,603,000	23,514,000	$ 159,011,000
Transactions costs																	$ 12,700,000
Amortization														(1,100,000)	6,900,000
Debt conversion amount		$ 79,800,000		$ 4,900,000	$ 55,700,000									4,911,000	$ 135,497,000
Percent of principal converted		50.00%			70.00%
Number of shares issued on conversion of debt (in shares)		35,300,000		1,800,000	20,500,000										56,600,000
Number of shares issued on conversion price excluding share issued for accrued interest (in shares)		25,600,000			17,900,000
Number of shares issued for accrued interest (in shares)		872,000
Five day average conversion price for accrued interest (in dollars per share)		$ 2.81
Common stock issued for interest on Notes		$ 2,400,000
Amortization of deferred debt costs and debt discount		$ 3,600,000			$ 2,000,000									$ 1,139,000	$ 6,921,000
Debt conversion per original conversion price (in shares)				1,600,000					200,000	2,600,000
Debt conversion expense									$ 1,200,000	$ 14,500,000			$ 25,600,000