Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Preferred Stock	Paid-In Capital	Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2014	$ 136,909	$ 16	$ 1	$ 286,006	$ 5,420	$ (154,534)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Options exercised	61			61
Retirement of shares upon vesting of restricted stock	(451)	0		(451)
Share-based compensation expense	4,617			4,617
Issuance of shares under employee stock purchase plan	199			199
Derivative fair value adjustment, net of tax	(4,473)				(4,473)
Preferred stock dividend	(5,139)					(5,139)
Net loss	(294,790)					(294,790)
Ending balance at Dec. 31, 2015	(163,067)	16	1	290,432	947	(454,463)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares in debt exchange	12,525	5		12,520
Retirement of shares upon vesting of restricted stock	(200)	0		(200)
Share-based compensation expense	1,444			1,444
Issuance of shares under employee stock purchase plan	145			145
Derivative fair value adjustment, net of tax	(5,697)				(5,697)
Preferred stock dividend	(5,349)					(5,349)
Net loss	(90,896)					(90,896)
Ending balance at Dec. 31, 2016	(251,095)	21	1	304,341	(4,750)	(550,708)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares	7,446	5		7,441
Retirement of shares upon vesting of restricted stock	(10)	0		(10)
Share-based compensation expense	1,447			1,447
Issuance of shares under employee stock purchase plan	25			25
Derivative fair value adjustment, net of tax	5,028				5,028
Preferred stock dividend	(5,139)					(5,139)
Net loss	(6,637)					(6,637)
Ending balance at Dec. 31, 2017	$ (248,935)	$ 26	$ 1	$ 313,244	$ 278	$ (562,484)