Property Dispositions - Narrative (Details) $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2018 Property	Dec. 31, 2019 USD ($) Bed	Dec. 31, 2018 USD ($) Bed Property	Dec. 31, 2017 USD ($) Bed Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total proceeds from disposition of real estate		$ 108,562	$ 242,284	$ 24,462
Number of beds | Bed		112,800
Loss from disposition of real estate		$ 53	(42,314)	632
Provision for impairment		17,214	0	15,317
Allianz Real Estate
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash contribution			$ 373,100
ACC/Allianz Joint Venture | Allianz Real Estate
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Minority interest (percent)			45.00%
Disposal group, not discontinued operations | Owned Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale price of disposed property		109,500		25,000
Total proceeds from disposition of real estate		$ 108,600		$ 24,500
Number of properties sold | Property			3	1
Number of beds | Bed			1,338	657
Gross proceeds from sale of portfolio			$ 245,000
Net proceeds from sale of portfolio			242,300
Gain on disposition of real estate			$ 42,300
Loss from disposition of real estate				$ 600
Provision for impairment				$ 4,900
Disposal group, not discontinued operations | Owned Properties | ACC/Allianz Joint Venture Transaction
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | Property	7		7
Number of beds | Bed			4,611
ACC/Allianz Joint Venture Transaction
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from secured debt issuance			$ 330,000