Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Carrying Amount
Unsecured notes payable		$ 1,518,657	$ 1,518,108
Variable rate debt		278,610	278,610
Mortgage notes payable		646,512	654,590
Mortgage note receivable	[1]	0	88,000
Fair Value
Unsecured notes payable		1,564,314	1,593,212
Variable rate debt		257,443	257,188
Mortgage notes payable		679,363	707,241
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