Subsequent Events Preferred Shares Redemption (Details) - USD ($)			1 Months Ended			12 Months Ended
		Feb. 23, 2017	Jan. 31, 2017	Feb. 29, 2012	[1]	Dec. 31, 2016	Dec. 31, 2015	Feb. 13, 2017	Oct. 31, 2015	May 31, 2014	Apr. 30, 2013
Subsequent Event [Line Items]
Stated liquidation value per share (in dollars per share)						$ 25.00
Series D Preferred Stock
Subsequent Event [Line Items]
Dividend rate (percent)				6.625%		6.625%	6.625%
Series D Preferred Stock | Subsequent Event
Subsequent Event [Line Items]
Dividend rate (percent)	[1]		6.625%
Scenario, Forecast | Series D Preferred Stock
Subsequent Event [Line Items]
Stated liquidation value per share (in dollars per share)		$ 25.00
Aggregate redemption price (in USD per share)		$ 25.3128472
Preferred stock redemption discount		$ 9,855,000
Forward Swap
Subsequent Event [Line Items]
Notional amount						$ 180,000,000			$ 300,000,000	$ 225,000,000	$ 240,000,000
Forward Swap | Subsequent Event
Subsequent Event [Line Items]
Notional amount								$ 125,000,000

[1] Holders are entitled to receive, when and as authorized by the Board of Directors, cumulative preferential cash dividends.