Co-investments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Equity Method Investment, Summarized Financial Information, Assets [Abstract]
Real estate under development	$ 226,690		$ 226,690		$ 429,096
Equity Method Investment, Summarized Financial Information, Liabilities and Equity [Abstract]
Other liabilities	34,722		34,722		32,444
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Interest expense	(50,053)	$ (45,830)	(148,401)	$ (117,021)
General and administrative	(11,129)	(11,479)	(31,223)	(28,621)
Equity income in co-investments	7,179	4,910	15,962	21,065
Total co investment [Member]
Equity Method Investment, Summarized Financial Information, Assets [Abstract]
Real estate under development	3,281,309		3,281,309		3,426,574
Other assets	117,430		117,430		107,902
Total assets	3,398,739		3,398,739		3,534,476
Equity Method Investment, Summarized Financial Information, Liabilities and Equity [Abstract]
Debt	1,423,734		1,423,734		1,568,398
Other liabilities	109,504		109,504		91,579
Equity	1,865,501		1,865,501		1,874,499
Total liabilities and equity	3,398,739		3,398,739		3,534,476
Company's share of equity	1,036,043		1,036,043		$ 1,042,423
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Property revenues	65,869	51,725	191,458	128,469
Property operating expenses	(23,094)	(18,759)	(69,232)	(48,875)
Net operating income	42,775	32,966	122,226	79,594
Gain on sale of real estate	0	0	14	11,369
Interest expense	(11,314)	(9,838)	(33,727)	(25,283)
General and administrative	(1,335)	(1,840)	(4,414)	(5,039)
Equity income in co-investments	0	4,808	0	14,351
Depreciation and amortization	(26,574)	(21,357)	(76,220)	(49,935)
Net income	3,552	4,739	7,879	25,057
Company's share of net income	7,179	4,910	15,962	21,065
Total co investment [Member] | Affiliated Entity [Member]
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Company's share of net income	$ 800	$ 1,100	$ 2,900	$ 2,900