Acquisitions, Dispositions and Other Significant Transactions - Blackstone Disposition (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) community	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of assets, net	$ 9,833	$ (233)	$ 76,586	$ (1,383)
Joint Venture | Blackstone Venture
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity interest sold	15.00%		15.00%
Payment to complete sale of joint venture interest	$ 2,000
Gain (loss) on sale of assets, net	$ 3,800		$ 3,800
2 Leased Communities Owned By Joint Venture Terminated | Blackstone Venture
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community	2