Acquisitions, Dispositions and Other Significant Transactions - 2015 Transactions (Details) $ in Thousands				1 Months Ended		3 Months Ended								12 Months Ended
	May 01, 2015 USD ($) community	Dec. 31, 2014 USD ($) community	Dec. 29, 2014 USD ($)	Oct. 31, 2015 USD ($) community	Feb. 28, 2015 USD ($) community	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) community	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($) community	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) community	Dec. 31, 2015 USD ($) community
Business Acquisition [Line Items]
Number of communities purchased or sold | community													7
Loss on facility lease termination														$ 14,276	$ 0	$ 0
Proceeds from sale of assets													$ 46,700
Communities classified as held for sale | community										10					10	17
Assets held for sale						$ 106,435				$ 97,843				106,435	$ 97,843	$ 110,600
Long-term debt, less current portion						3,375,324				3,413,998				3,375,324	3,413,998
Asset impairment						18,966	$ 368,551	$ 1,559	$ 20,706	221,877	$ 19,111	$ 4,152	$ 3,375	409,782	248,515	$ 57,941
Goodwill						$ 505,783				$ 705,476				$ 505,783	$ 705,476
Communities sold during 2015
Business Acquisition [Line Items]
Number of communities disposed of | community																17
Proceeds from sale of assets																$ 82,900
Asset impairment																18,400
HCP Community Acquisitions
Business Acquisition [Line Items]
Number of communities purchased or sold | community	1	8
Aggregate purchase price	$ 8,600	$ 51,400	$ 60,000
February 2015 acquisition of 15 communities
Business Acquisition [Line Items]
Number of communities purchased or sold | community					15
Aggregate purchase price					$ 268,600
Fair value of assets acquired					187,200
Loss on facility lease termination					76,100
Reversal of deferred lease liability					$ 5,300
Seller Financed Debt
Business Acquisition [Line Items]
Principal Amount																$ 20,000
Loan term																5 years
Seller financing fixed rate																8.00%
5 Communities acquired in October 2015
Business Acquisition [Line Items]
Number of communities purchased or sold | community				5
Aggregate purchase price				$ 78,400
Minimum | February 2015 acquisition of 15 communities
Business Acquisition [Line Items]
Cap rate					6.25%
Maximum | February 2015 acquisition of 15 communities
Business Acquisition [Line Items]
Cap rate					8.75%
Assets held for sale
Business Acquisition [Line Items]
Communities classified as held for sale | community																17
Long-term debt, less current portion																$ 60,800
Asset impairment																15,200
Goodwill																$ 8,100