Equity - Class of Stock Disclosures - Dividends and AOCI (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended							3 Months Ended		6 Months Ended
	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Apr. 30, 2016	Jun. 30, 2015	May 31, 2015	Apr. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Dividend Distributions
Declared		$ 41,031			$ 37,883			$ 41,031	$ 37,883	$ 41,031	$ 37,883
Paid										$ 41,031	$ 37,883
Dividends declared and paid per common share per month (in dollars per share)		$ 0.18	$ 0.18	$ 0.18	$ 0.17	$ 0.17	$ 0.17
Dividends per share declared (in dollars per share)								$ 0.54	$ 0.51	$ 1.08	$ 1.02
Accumulated other comprehensive income
Accumulated other comprehensive income		$ 13						$ 13		$ 13		$ 47
Subsequent Event | Dividend Payable, July 29, 2016
Dividend Distributions
Dividends per share declared (in dollars per share)	$ 0.18
Subsequent Event | Dividend Payable, August 31, 2016
Dividend Distributions
Dividends per share declared (in dollars per share)	0.18
Subsequent Event | Dividend Payable, September 30, 2016
Dividend Distributions
Dividends per share declared (in dollars per share)	$ 0.18
Series C Preferred Stock
Dividend Distributions
Declared					$ 1,636				$ 1,636		$ 1,636
Paid											1,636
Common Stock
Dividend Distributions
Declared		$ 41,031			$ 36,247			$ 41,031	$ 36,247	41,031	36,247
Paid										$ 41,031	$ 36,247