Co-investments - Summary of Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 1,307,561	$ 1,300,140
Total operating and other co-investments, net [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 802,334	833,270
Membership Interest In CPPIB [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	54.00%
Co-investments	$ 478,440	482,507
Membership interest in Wesco I, III, IV, and V [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	52.00%
Co-investments	$ 191,205	194,890
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	$ 118,982	121,780
Membership In Other [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	49.00%
Co-investments	$ 13,707	34,093
Total development co-investments, net [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	50.00%
Co-investments	$ 109,696	94,060
Total preferred interest co-investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	395,531	372,810
Total preferred interest co-investments [Member] | Investments in Majority-owned Subsidiaries [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 67,000	$ 51,800