Summary of Significant Accounting Policies (Details 4) (Preferred stock, USD $)	12 Months Ended
	Dec. 31, 2014
Series A
Preferred stock
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 10.00
Preferred stock dividend rate (as a percent)	5.00%
Series B
Preferred stock
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 10.00
Preferred stock dividend rate (as a percent)	5.00%
Series C
Preferred stock
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 13.00
Preferred stock conversion price (In dollars per share)	$ 13.00
Preferred stock dividend rate (as a percent)	5.00%
Series D
Preferred stock
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 1,000
Preferred stock dividend rate (as a percent)	5.00%
Series E
Preferred stock
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 1,000
Preferred stock dividend rate (as a percent)	5.00%