Co-investments - Summary of Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 1,290,957	$ 1,119,258
Total operating and other co-investments, net [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 896,545	780,332
Membership Interest In CPPIB [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	54.00%
Co-investments	$ 496,512	500,287
Membership interest in Wesco I, III, IV, and V [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	53.00%
Co-investments	$ 214,650	214,408
Membership interest in BEXAEW, BEX II And BEX III [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	50.00%
Co-investments	$ 135,174	13,827
Membership In Other [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	52.00%
Co-investments	$ 50,209	51,810
Total development co-investments, net [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	50.00%
Co-investments	$ 75,092	73,770
Total preferred interest co-investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	319,320	265,156
Total preferred interest co-investments [Member] | Investments in Majority-owned Subsidiaries [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 15,600	15,700
BEX II [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments		$ (36,700)