Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Carrying Amount
Unsecured notes payable		$ 1,518,931	$ 1,518,108
Variable rate debt		278,610	278,610
Mortgage notes payable		642,396	654,590
Fair Value
Unsecured notes payable		1,552,682	1,593,212
Variable rate debt		254,405	257,188
Mortgage notes payable		673,959	707,241
Financing Receivable, Net	[1]	0	88,000
Mortgage note receivable	[1]	$ 0	$ 87,692

[1] On January 30, 2015 the mortgage note was repaid. For further information regarding the mortgage note, see Note 2, "Summary of Significant Accounting Policies," included in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2014