Line Of Credit Payable (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	May 31, 2011
Line of Credit Facility [Abstract]
Revolving credit facility original borrowing capacity			$ 400,000
Revolving credit facility borrowing capacity			450,000
Revolving credit facility weighted average outstanding balance	52,946
Revolving credit facility weighted average interest rate	1.80%
Maturity date	May 2015
Option to extend maturity date	May 2016.
Debt instrument, description of variable rate basis	LIBOR plus 150
Option to increase facility size	650,000
Line of credit payable	142,600	65,600
Line of credit facility available for future borrowings	307,400
Line of credit facility undrawn letters of credit	$ 3,800