Stockholders' Equity (Deficit) (Details) (USD $)	12 Months Ended						0 Months Ended		1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Series A Preferred Stock	Dec. 31, 2011 Series A Preferred Stock	May 31, 2012 Series A Preferred Stock	Dec. 05, 2012 Common Stock	May 03, 2012 Common Stock	Jan. 31, 2013 Common Stock	Dec. 31, 2012 Common Stock item	May 31, 2012 Common Stock
Stockholders' equity
Number of outstanding shares of Series A preferred Stock that are automatically converted to shares of common stock	0	49,000,000				49,000,000
Number of shares of common stock into which Series A preferred stock automatically got converted											12,249,998
Rate at which dividends accrued (in dollars per share)				$ 0.07
Accumulated dividends				$ 0	$ 20,500,000
Number of votes to which holders of common shares are entitled for each share held										1
Number of shares sold							6,000,000	10,000,000
Selling price (in dollars per share)							$ 8	$ 5	$ 8
Expenses incurred in connection with offering							3,300,000	4,700,000
Shares of common stock sold upon exercise of full amount of over-allotment option by the underwriters								449,250	239,432
Gross proceeds from issuance of common stock								52,300,000
Net cash proceeds from sale of common stock	29,000	29,000	4,000					47,600,000
Gross cash proceeds from sale of common stock in a follow-on offering							49,900,000
Net cash proceeds from sale of common stock in a follow-on offering							$ 46,600,000