Co-investments - Summary of Investments (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 1,122,913	$ 1,036,047
Total operating co investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	794,858	831,521
Membership Interest In Limited Liability Company That Owns Connolly Station [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 426,259	422,317
Limited partnership interest in partnership investments	55.00%
Membership interest in Wesco I, III, and IV [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 202,531	218,902
Limited partnership interest in partnership investments	50.00%
Membership interest in BEXAEW [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 66,346	88,850
Limited partnership interest in partnership investments	50.00%
Membership Interest In Palm Valley [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 68,403	68,525
Limited partnership interest in partnership investments	50.00%
Partnership interest in Other Funds [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 31,319	32,927
Partnership interest in Other Funds [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	50.00%
Partnership interest in Other Funds [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	55.00%
Total development co investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 141,666	98,214
Total development co investments [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	50.00%
Total development co investments [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	55.00%
Total preferred interest investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 186,389	106,312
Total preferred interest investments [Member] | Investments in Majority-owned Subsidiaries [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 35,900	$ 35,800