Shareholders' Equity (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Class of Stock [Line Items]
Preferred Stock, Liquidation Preference Per Share	$ 25.00	$ 25.00
Preferred Stock, Dividend Payment Terms	October 14, 2016
Balance as of beginning of period		49,047,335	54,739,111
Common stock issued under DRIP		15,714	16,862
Common stock issued under stock and incentive plans		214,878	263,829.000
Common stock forfeited for tax withholding on share-based compensation		(80,888)	(67,296)
Common stock repurchased during the period		(48,444)	(4,383,716)
Balance as of end of period	49,148,595	49,148,595	50,568,790
Dividend reinvestment plan, shares authorized	3,000,000	3,000,000
Stock issued during period, remaining shares available, dividend reinvestment plan	2,411,824	2,411,824
Dividends declared per common share	$ 0.21
Stock Repurchase Program, Authorized Amount	$ 50,000,000	$ 50,000,000
Stock Repurchase Program Expiration Date		Dec. 31, 2016
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 8,518,000	$ 8,518,000
Series A Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage		8.50%
Preferred Stock, Shares Issued	2,300,000	2,300,000		2,300,000
Series B Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage		7.625%
Preferred Stock, Shares Issued	2,250,000	2,250,000		2,250,000
Preferred Stock
Class of Stock [Line Items]
Dividends Payable, Date of Record	Oct. 01, 2016
Common Stock
Class of Stock [Line Items]
Dividends Payable, Date of Record	Oct. 05, 2016
Dividends Payable, Date to be Paid	Oct. 31, 2016
Common Stock | At the market progam [Member]
Class of Stock [Line Items]
ATM program, authorized shares remaining	7,416,520	7,416,520