Fair Value Measurements (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Fair Value Measurements [Abstract]
Marketable securities (1)		$ 24,251	$ 90,235
Marketable securities, Estimated Fair Value	[1]	24,305	90,035
Notes payable (2)		3,768,945	3,171,742
Notes payable, Estimated Fair Value	[2]	3,850,948	3,313,936
Mortgages payable (3)		1,768,827	1,424,228
Mortgages payable, Estimated Fair Value	[3]	$ 1,815,721	$ 1,481,138

[1] As of June 30, 2015 and December 31, 2014, the Company determined that $22.5 million and $87.7 million, respectively, of the Marketable securities estimated fair value were classified within Level 1 of the fair value hierarchy and the remaining $1.8 million and $2.3 million, respectively, were classified within Level 3 of the fair value hierarchy.

[2] The Company determined that its valuation of Notes payable was classified within Level 2 of the fair value hierarchy.

[3] The Company determined that its valuation of Mortgages payable was classified within Level 3 of the fair value hierarchy.