Equity and Capital Equity and Capital - Common Stock (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Aug. 06, 2013	Aug. 10, 2013 Maximum	Sep. 30, 2013 Restricted Stock [Member]	Sep. 30, 2013 Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2012 Accumulated Other Comprehensive Income (Loss) [Member]	Sep. 30, 2013 Loss on Settlement of Derivative Instruments [Member]	Dec. 31, 2012 Loss on Settlement of Derivative Instruments [Member]	Sep. 30, 2013 Fair Value of Derivative Instruments [Member]	Dec. 31, 2012 Fair Value of Derivative Instruments [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	30	1,899
Accumulated other comprehensive loss						$ (28,430,000)	$ (57,715,000)	$ (54,905,000)	$ (61,991,000)	$ 26,475,000	$ 4,276,000
Equity Issuances, Amount Available for Issuance	198,400,000	198,400,000		200,000,000
Weighted Average Price Per Share	$ 52.28	$ 53.35
Net proceeds from common stock issuance	1,568,000	101,342,000	121,800,000
Payments of Stock Issuance Costs	69,000	69,000
Payments for Commission Expense	$ 24,000	$ 1,520,000
Weighted average grant date fair value (in dollars per share)					$ 52.80