Consolidated Statements of Shareholders' Equity (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Total	Preferred Shares	Common Shares	Additional Paid-In Capital	Cumulative Dividends in Excess of Net Income	Accumulated Other Comprehensive Loss
Balance, beginning at Dec. 31, 2011	$ 520,129	$ 0	$ 322	$ 543,861	$ (22,924)	$ (1,130)
Beginning balance, common shares, shares outstanding at Dec. 31, 2011	32,161,620		32,161,620
Beginning balance, preferred shares, shares outstanding at Dec. 31, 2011	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Sale of common shares, net of underwriting fees and offering costs (in shares)			7,475,000
Sale of common shares, net of underwriting fees and offering costs, value	132,600		75	132,525
Sale of preferred shares, net of underwriting fees and offering costs (in shares)		5,000,000
Sale of preferred shares, net of underwriting fees and offering costs, value	120,581	50		120,531
Repurchase of common shares	(621)		(1)	(620)
Repurchase of common shares (in shares)	(36,008)		(36,008)
Issuance of restricted common shares (in shares)	6,500		6,500
Issuance of unrestricted common shares, value	60			60
Issuance of unrestricted common shares (in shares)	3,281		3,281
Amortization of deferred compensation	2,288			2,288
Declaration of dividends on common shares	(22,851)				(22,851)
Declaration of dividends on preferred shares	(2,368)				(2,368)
Net income	17,290				17,290
Other comprehensive income	54					54
Balance, ending at Sep. 30, 2012	$ 767,162	$ 50	$ 396	$ 798,645	$ (30,853)	$ (1,076)
Ending balance, common shares, shares outstanding at Sep. 30, 2012	39,610,393
Ending balance, preferred shares, shares outstanding at Sep. 30, 2012	5,000,000