Equity (Series D Preferred Stock) (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions			12 Months Ended
	Sep. 02, 2014	Nov. 12, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jul. 20, 2015
Class of Stock [Line Items]
Common stock, par value (in dollars per share)			$ 0.01	$ 0.01		$ 0.01
Proceeds from issuances of common stock			$ 0	$ 1,595,045	$ 1,993,159
Cash redemption of preferred stock			$ 0	316,126	$ 0
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Common stock, par value (in dollars per share)					$ 0.01
Temporary equity (in shares)		21.7
Proceeds from issuances of preferred shares		$ 288,000
Preferred stock, dividend rate					5.81%
Dividends paid (in dollars per share)					$ 13.59
Temporary equity dividend rate per dollar amount (in dollars per share)					$ 0.79
Cash redemption of preferred stock	$ 316,100
Fair value		$ 18,700			$ 16,700
Loss on derivative instruments				$ 13,600	$ 2,000
Common Stock [Member]
Class of Stock [Line Items]
Common stock, par value (in dollars per share)					$ 0.01
Temporary equity (in shares)		15.1
Proceeds from issuances of common stock		$ 186,000