Notes Payable (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Notes Payable [Line Items]
Notes payable	$ 724,136	$ 654,098
6.3% Senior Notes [Member]
Notes Payable [Line Items]
Notes payable	299,136	299,098
$600 Million Revolving Loan Facility [Member]
Notes Payable [Line Items]
Notes payable	$ 425,000	$ 355,000