Co-investments - Combined Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Equity Method Investment, Summarized Financial Information, Assets [Abstract]
Rental properties and real estate under development	$ 562,338		$ 562,338		$ 454,629
Other liabilities	36,128		36,128		33,375
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Interest expense	(54,896)	$ (55,196)	(162,651)	$ (166,335)
General and administrative	(11,345)	(10,601)	(38,731)	(36,539)
Total co investment [Member]
Equity Method Investment, Summarized Financial Information, Assets [Abstract]
Rental properties and real estate under development	4,779,685		4,779,685		4,367,987
Other assets	110,364		110,364		104,119
Total assets	4,890,049		4,890,049		4,472,106
Debt	2,316,618		2,316,618		2,190,764
Other liabilities	146,643		146,643		106,316
Equity	2,426,788		2,426,788		2,175,026
Total liabilities and equity	4,890,049		4,890,049		4,472,106
Company's share of equity	1,413,861		1,413,861		$ 1,300,140
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Property revenues	84,071	84,820	249,628	247,010
Property operating expenses	(29,214)	(27,779)	(85,768)	(81,415)
Net operating income	54,857	57,041	163,860	165,595
Interest expense	(16,089)	(15,805)	(47,284)	(46,179)
General and administrative	(2,603)	(1,254)	(6,774)	(5,134)
Depreciation and amortization	(30,411)	(32,833)	(89,283)	(95,312)
Net income	5,754	7,149	20,519	18,970
Company's share of net income	21,700	16,788	54,935	64,611
Total co investment [Member] | Affiliated Entity [Member]
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Company's share of net income	$ 2,000	$ 700	$ 5,500	$ 1,400