Debt (Narratives) (Details) (USD $)	6 Months Ended			0 Months Ended	6 Months Ended			1 Months Ended				6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jul. 31, 2013 Bank of America	Jun. 30, 2013 Fixed Interest Rate Loans	Jun. 30, 2013 Variable Interest Rate Loans	Jun. 30, 2013 Domestic	Jul. 31, 2013 Revolving Credit Facility	Jun. 30, 2013 Revolving Credit Facility	Feb. 29, 2012 Revolving Credit Facility	Jun. 30, 2013 Term Loan Facility	Jun. 30, 2013 Senior Credit Facility	Jul. 31, 2013 Unsecured Term Loan
Revolving Line Of Credit
Senior credit facility				$ 300,000,000					$ 450,000,000	$ 450,000,000	$ 175,000,000	$ 625,000,000	$ 300,000,000
Credit facility, expiration date				Jul. 31, 2014								Dec. 31, 2014
Credit facility, interest rate at end of period												1.75%
Letters of credit outstanding amount												2,400,000
Credit facililty potential increase												125,000,000
Interest rate on debt				1.60%
Debt instrument, covenant compliance												We were in compliance with all of these covenants at June 30, 2013.
Amount Outstanding									210,000,000		175,000,000	385,000,000	300,000,000
Payment of outstanding debt	98,000,000	15,000,000						250,000,000
Non Recourse Debt
Amount of debt acquired							36,500,000
Collateral mortgage loan, carrying value	2,400,000,000		2,400,000,000
Mortgage loan on real estate, minimum interest rate					2.70%	1.20%
Mortgage loan on real estate, maximum interest rate					10.00%	7.60%
Debt instrument maturity date, range start	Jul. 01, 2013
Debt instrument maturity date, range end	Sep. 01, 2026
Mortgage loans on real estate, interest rate	5.00%						4.05%
Debt refinanced	41,500,000
Debt refinanced, restated carrying value	$ 62,500,000
Mortgage loan term	10						10