Common Stock and Dividends (Details) (USD $)	0 Months Ended				3 Months Ended
	Apr. 17, 2015	Apr. 09, 2015	Oct. 15, 2014	Apr. 18, 2014	Mar. 31, 2015	May 01, 2015	Apr. 09, 2015
Common Stock and Dividends
Series A cumulative perpetual preferred shares, outstanding					216,000
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					10 years
Cash dividends (as a percent)					33.00%
Cash dividends paid to common shareholders (in dollars per share)	$ 0.29		$ 0.27	$ 0.25
Repurchase of common stock, authorized amount					$ 40,000,000		$ 40,000,000
Period of repurchase of common stock		12 months			12 months
Cumulative number of shares repurchased under all stock repurchase programs						8,684,680
Cumulative cost of shares repurchased under all stock repurchase programs						$ 257,704,000