Co-investments - Summary of Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 1,069,684	$ 1,036,047
Total operating co investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 771,293	786,066
Total operating co investments [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	50.00%
Total operating co investments [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	55.00%
Membership Interest In Limited Liability Company That Owns Connolly Station [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 380,399	376,862
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	$ 216,485	218,902
Limited partnership interest in partnership investments	50.00%
Membership interest in BEXAEW [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 74,069	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	$ 68,340	68,525
Limited partnership interest in partnership investments	50.00%
Partnership interest in Fund II [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 32,000	32,927
Partnership interest in Fund II [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	50.00%
Partnership interest in Fund II [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	$ 158,408	143,669
Total preferred interest investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	139,983	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