Shareholders' Equity (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Class of Stock [Line Items]
Preferred Stock, Liquidation Preference Per Share	$ 25.00	$ 25.00
Balance as of beginning of period		49,047,335	54,739,111
Common stock issued under DRIP		12,206	9,688
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)	(860,721)
Balance as of end of period	49,145,087	49,145,087	54,084,611
Dividend reinvestment plan, shares authorized	3,000,000	3,000,000
Stock issued during period, remaining shares available, dividend reinvestment plan	2,415,332	2,415,332
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	$ 9,000	$ 9,000
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
Common Stock | At the market progam [Member]
Class of Stock [Line Items]
ATM program, authorized shares remaining	7,416,520	7,416,520