Stockholders' Equity - Dividend Transactions (Details) - USD ($)												3 Months Ended
	Mar. 28, 2016	Mar. 27, 2016	Mar. 15, 2016	Mar. 13, 2016	Feb. 27, 2016	Feb. 26, 2016	Feb. 15, 2016	Feb. 13, 2016	Jan. 27, 2016	Jan. 16, 2016	Jan. 15, 2016	Mar. 31, 2016	Mar. 31, 2015
Class of Stock [Line Items]
Common stock dividends cash paid (in dollars per share)		$ 0.33			$ 0.33				$ 0.33
Aggregate amount paid to holders of record (in dollars)		$ 12,131,000			$ 12,131,000				$ 12,131,000			$ 36,393,000	$ 42,486,000
Common stock dividends declared per common share (in dollars per share)				$ 0.33				$ 0.33			$ 0.33	$ 0.99	$ 0.96
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends cash paid (in dollars per share)	$ 0.171875					$ 0.171875			$ 0.171875
Aggregate amount paid to holders of record (in dollars)	$ 374,800					$ 374,800			$ 374,800			$ 1,124,400	$ 1,124,000
Preferred stock dividends declared per common share (in dollars per share)			$ 0.17				$ 0.17				$ 0.17
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends cash paid (in dollars per share)	$ 0.1640625					$ 0.1640625			$ 0.1640625
Aggregate amount paid to holders of record (in dollars)	$ 927,000					$ 927,000			$ 927,000			$ 2,781,000	$ 2,781,000
Preferred stock dividends declared per common share (in dollars per share)			$ 0.16				$ 0.16			$ 0.16