Shareholders' Equity (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Class of Stock [Line Items]
Preferred Stock, Liquidation Preference Per Share	$ 25.00
Shareholders' Equity, Common Stock [Roll Forward]
Balance as of beginning of period	49,047,335	54,739,111
Common stock issued under DRIP	9,074	4,744
Common stock issued or redeemed under stock and incentive plans	168,720	231,274
Common stock forfeited for tax withholding on share-based compensation	(80,888)	(65,913)
Common stock repurchased during period	(48,444)	(16,140)
Balance as of end of period	49,095,797	54,893,076
Dividend reinvestment plan, shares authorized	3,000,000
Stock issued during period, remaining shares available, dividend reinvestment plan	2,418,464
Dividends declared per common share	$ 0.21
Stock Repurchase Program, Authorized Amount	$ 50,000,000
Stock Repurchase Program Expiration Date	Dec. 31, 2016
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 8,518,000
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	8.50%
Preferred Stock, Shares Issued	2,300,000		2,300,000
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	7.625%
Preferred Stock, Shares Issued	2,250,000		2,250,000
Common Stock [Member] | At the market progam [Member]
Shareholders' Equity, Common Stock [Roll Forward]
ATM program, authorized shares remaining	7,416,520