Line Of Credit Payable (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Oct. 31, 2012	Dec. 31, 2011	Sep. 30, 2010
Line of Credit Facility [Abstract]
Revolving credit facility original borrowing capacity				$ 450,000,000
Revolving credit facility borrowing capacity		500,000,000
Revolving credit facility weighted average outstanding balance	53,419,000
Revolving credit facility weighted average interest rate	1.70%
Spread over LIBOR	11.75%
Option to increase facility size	1,000,000,000
Line of credit payable	174,200,000		65,600,000
Line of credit facility available for future borrowings	325,800,000
Line of credit facility undrawn letter of credit	$ 3,800,000