Preferred Stock, Common Stock and Dividends (Details) (USD $)	1 Months Ended					3 Months Ended
	Apr. 30, 2012	Oct. 31, 2011	Apr. 30, 2011	Feb. 28, 2011	Apr. 30, 2009	Mar. 31, 2012 Y	Mar. 31, 2011	Dec. 31, 2011	May 15, 2011	Mar. 10, 2011 month	Apr. 07, 2009 month	Dec. 23, 2008
Preferred Stock, Common Stock and Dividends
Series A cumulative perpetual preferred shares, issued						216,000		216,000
Series A Cumulative perpetual preferred shares, par value (in dollars per share)						$ 0.01		$ 0.01
Series A Cumulative perpetual preferred shares, per share liquidation value (in dollars per share)						$ 1,000		$ 1,000
Series A cumulative perpetual preferred shares, aggregate liquidation value						$ 216,000,000
Senior preferred stock, dividend rate for first five years (as a percent)						5.00%
Senior preferred stock, dividend rate thereafter (as a percent)						9.00%
Warrants to purchase entity's common stock (in shares)						1,326,238
Warrants, exercise price (in dollars per share)						$ 24.43
Percentage of aggregate common stock investment on exercise of warrant to Senior Preferred Stock investment						15.00%
Warrants, term (in years)						10
Senior preferred stock, dividend paid				2,700,000
Senior preferred stock, future payment									2,700,000
Series A cumulative perpetual preferred shares, fair value as if issued on a stand-alone basis						130,900,000
Warrants, fair value as if issued on a stand-alone basis						8,000,000
Series A Cumulative perpetual preferred shares, discount (in dollars)						4,809,000		5,452,000				12,400,000
Period of amortization of discount on preferred shares (in years)						5
Amortization of discount on series A cumulative perpetual preferred shares						643,000	605,000
Cash dividends paid to common shareholders (in dollars per share)	$ 0.20	$ 0.19	$ 0.19
Repurchase of common stock, authorized amount					40,000,000	40,000,000
Period of repurchase of common stock (in months)										12	12
Cumulative number of shares repurchased under all stock repurchase programs						7,777,293
Cumulative cost of shares repurchased under all stock repurchase programs						$ 236,378,000