Notes Payable (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Notes Payable [Line Items]
Notes payable	$ 393,714	$ 298,637
6.3% Senior Notes [Member]
Notes Payable [Line Items]
Notes payable	298,714	298,637
$600 Million Revolving Loan Facility [Member]
Notes Payable [Line Items]
Notes payable	$ 95,000