Investments in Partially Owned Entities - Consolidated Variable Interest Entities ("VIEs") - Additional Information (Details) $ in Thousands	Mar. 31, 2019 USD ($) Property ApartmentUnit	Dec. 31, 2018 USD ($)
Variable Interest Entity [Line Items]
Properties | Property	310
Apartment units | ApartmentUnit	80,061
Total assets	$ 20,768,811	$ 20,394,209
Total liabilities	$ 10,069,744	9,615,454
Consolidated VIE [Member]
Variable Interest Entity [Line Items]
Properties | Property	17
Apartment units | ApartmentUnit	3,535
Total assets	$ 694,700	713,600
Total liabilities	$ 316,100	$ 313,900