Stockholders' Equity (Details) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended			20 Months Ended	26 Months Ended
	Dec. 05, 2012 USD ($) $ / shares shares	May. 01, 2012 USD ($) $ / shares shares	Jan. 31, 2013 $ / shares shares	Dec. 31, 2015 USD ($) item shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) item shares
Stockholders' equity
Expenses incurred in connection with offering						$ 869
Gross cash proceeds from sale of common stock in a follow-on offering				$ 1,867	$ 571	$ 2,437
7.50% Convertible Senior Secured Notes due 2019
Stockholders' equity
Shares of common stock issued in conversion of Notes | shares				5,200,000	2,500,000			15,372,477
Principal amount of the Notes converted				$ 27,522	$ 13,400		$ 53,941	$ 81,500
Shares of common stock issued in settlement of the interest make-whole provision | shares				500,000	400,000			2,195,904
Common Stock
Stockholders' equity
Number of votes to which holders of common shares are entitled for each share held | item				1				1
Number of shares sold | shares	6,000,000	10,000,000
Selling price (in dollars per share) | $ / shares	$ 8	$ 5	$ 8
Expenses incurred in connection with offering	$ 3,300	$ 4,700
Shares of common stock sold upon exercise of full amount of over-allotment option by the underwriters | shares		449,250	239,432
Gross proceeds from issuance of common stock		$ 52,300
Net cash proceeds from sale of common stock		$ 47,600
Gross cash proceeds from sale of common stock in a follow-on offering	49,900
Net cash proceeds from sale of common stock in a follow-on offering	$ 46,600