Notes Payable (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Notes Payable [Line Items]
Notes payable	$ 909,328	$ 824,251
6.3% Senior Notes [Member]
Notes Payable [Line Items]
Notes payable	299,328	299,251
Revolving Loan Facility [Member]
Notes Payable [Line Items]
Notes payable	$ 610,000	$ 525,000