Notes Payable (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Notes Payable [Line Items]
Notes payable	$ 618,982	$ 583,944
Senior Notes [Member]
Notes Payable [Line Items]
Notes payable	298,982	298,944
Revolving Credit Facility [Member]
Notes Payable [Line Items]
Notes payable	$ 320,000	$ 285,000