Significant Transactions - Summarized Information Regarding Acquisitions (Details) $ / shares in Units, $ in Thousands, shares in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) community apartment_home $ / shares shares
Business Acquisition [Line Items]
Number of apartment homes | community	6
Number of apartment communities | apartment_home	1,480
Purchase price	$ 483,066
Capitalized transaction costs	7,591
Total fair value allocated to land	69,177
Total fair value allocated to building and improvements	424,718
Total fair value allocated to intangible assets	9,700
Total fair value allocated to intangible liabilities	12,938
Philadelphia-Area Apartment Communities
Business Acquisition [Line Items]
Cash paid in acquisition	34,400
Property-level debt assumed in acquisition	$ 208,900
OP Units issued in acquisition (in shares) | shares	1.2
Share price per unit (in dollars per share) | $ / shares	$ 41.08