Co-investments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Equity Method Investment, Summarized Financial Information, Assets [Abstract]
Real estate under development	$ 220,911		$ 220,911		$ 429,096
Equity Method Investment, Summarized Financial Information, Liabilities and Equity [Abstract]
Other liabilities	34,669		34,669		32,444
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Interest expense	(50,802)	$ (42,151)	(98,348)	$ (71,192)
General and administrative	(9,549)	(9,558)	(20,094)	(17,141)
Equity income in co-investments	4,472	5,629	8,783	16,155
Total co investment [Member]
Equity Method Investment, Summarized Financial Information, Assets [Abstract]
Real estate under development	3,275,960		3,275,960		3,426,574
Other assets	110,690		110,690		107,902
Total assets	3,386,650		3,386,650		3,534,476
Equity Method Investment, Summarized Financial Information, Liabilities and Equity [Abstract]
Debt	1,391,474		1,391,474		1,568,398
Other liabilities	95,386		95,386		91,579
Equity	1,899,790		1,899,790		1,874,499
Total liabilities and equity	3,386,650		3,386,650		3,534,476
Company's share of equity	1,044,208		1,044,208		$ 1,042,423
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Property revenues	62,092	48,784	125,589	76,744
Property operating expenses	(23,184)	(18,556)	(46,138)	(30,116)
Net operating income	38,908	30,228	79,451	46,628
Gain on sale of real estate	0	0	14	11,369
Interest expense	(11,097)	(9,422)	(22,413)	(15,445)
General and administrative	(1,473)	(1,811)	(3,079)	(3,199)
Equity income in co-investments	0	4,784	0	9,543
Depreciation and amortization	(24,265)	(17,885)	(49,646)	(28,578)
Net income	2,073	5,894	4,327	20,318
Company's share of net income	$ 4,472	$ 5,629	$ 8,783	$ 16,155