Indebtedness Unsecured Debt (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Debt Instrument [Line Items]
Proceeds from unsecured debt	$ 500,000	$ 600,000
Repayments of Unsecured Debt	426,462	172,374
Variable Rate UnSecured Debt [Member] [Member]
Debt Instrument [Line Items]
Proceeds from unsecured debt	250,000
Fixed Rate Unsecured Debt [Member]
Debt Instrument [Line Items]
Proceeds from unsecured debt	250,000
Debt Instrument, Estimated Trading Values, Percent of Face Value, Minimum	93.00%
Debt Instrument, Estimated Trading Values, Percent of Face Value, Maximum	124.00%
Debt Instrument, Interest Rate, Stated Percentage	3.625%
Debt Instrument, Interest Rate, Effective Percentage	3.72%
number of unsecured notes repaid	2
Repayments of Unsecured Debt	$ 425,000
Debt Instrument, Covenant Compliance	We were in compliance with all such covenants at September 30, 2013
Fixed Rate Unsecured Debt Repaid [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.68%
Debt Instrument, Interest Rate, Effective Percentage	6.40%
Variable Rate Unsecured Debt [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Description of Variable Rate Basis	LIBOR
Debt Instrument, Basis Spread on Variable Rate	1.35%
Debt Instrument, Interest Rate at Period End	1.54%