Discontinued Operations - Additional Information (Detail) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) apartmentunits Communities	Dec. 31, 2014 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation and Amortization, Discontinued Operations	$ 2.3
Number Of Properties Sold | Communities	1
Number of Units in Real Estate Property | apartmentunits	79,977
Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Prior Period Reclassification Adjustment	$ 34.1	$ 36.5