Debt - Debt (Details) - Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations - Mortgage notes payable - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
32 Communities Held For Sale
Debt Instrument [Line Items]
Mortgage debt	$ 158.6
15 Communities Held For Sale
Debt Instrument [Line Items]
Mortgage debt		$ 30.1