Co-investments - Summary of Investments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 1,324,081	$ 1,300,140
Total operating and other co-investments, net [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 793,870	833,270
Membership Interest In CPPIB [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	54.00%
Co-investments	$ 473,746	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	$ 187,446	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	$ 117,607	121,780
Membership In Other [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments	49.00%
Co-investments	$ 15,071	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	$ 120,249	94,060
Total preferred interest co-investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	409,962	372,810
Total preferred interest co-investments [Member] | Investments in Majority-owned Subsidiaries [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 68,600	$ 51,800