Fair Value Measurements (Details 3) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair value of nonrecourse mortgage debt and notes payable (exclusive of fair value of derivatives), revolving credit facility and convertible senior debt [Abstract]
Carrying Value	$ 4,847,534	$ 4,938,201
Fair Value	5,109,899	5,346,196
Fixed Rate Debt [Member]
Fair value of nonrecourse mortgage debt and notes payable (exclusive of fair value of derivatives), revolving credit facility and convertible senior debt [Abstract]
Carrying Value	2,818,484	2,993,591
Fair Value	3,116,280	3,421,373
Variable Rate Debt [Member]
Fair value of nonrecourse mortgage debt and notes payable (exclusive of fair value of derivatives), revolving credit facility and convertible senior debt [Abstract]
Carrying Value	2,029,050	1,944,610
Fair Value	$ 1,993,619	$ 1,924,823