Leases and Management Agreements with Five Star - Narrative (Details) $ in Thousands			1 Months Ended							3 Months Ended								5 Months Ended	12 Months Ended
	Nov. 09, 2017 property	Jun. 29, 2016 USD ($) community pooling_agreement lease_agreement agreement	Nov. 30, 2017 pooling_agreement renewal_option	Dec. 31, 2016 USD ($) living_unit community	Dec. 31, 2016 USD ($) community	Jun. 30, 2016 pooling_agreement lease_agreement	Sep. 30, 2015 community	May 31, 2015 community	Feb. 28, 2015 USD ($)	Dec. 31, 2017 USD ($) living_unit community lease_agreement	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($) community	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) community	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2015 community	Dec. 31, 2017 USD ($) living_unit community lease_agreement	Dec. 31, 2017 USD ($) living_unit community lease_agreement	Dec. 31, 2017 USD ($) living_unit community lease_agreement	Dec. 31, 2017 USD ($) living_unit community lease_agreement	Dec. 31, 2017 USD ($) living_unit community lease_agreement management_agreement	Dec. 31, 2016 USD ($) community	Dec. 31, 2015 USD ($) community
Concentration Risk [Line Items]
Number of communities																					305
Revenues | $										$ 278,566	$ 266,679	$ 265,013	$ 264,561	$ 274,296	$ 263,983	$ 261,367	$ 258,375			$ 1,074,819				$ 1,058,022	$ 998,773
Real estate improvements by lessee purchased | $																				51,952				30,328
Increase (decrease) in annual lease rent payable | $																				$ 4,870				2,393
Senior Living Communities
Concentration Risk [Line Items]
Number of communities																		19
Related Party Transaction, Number Of Subleases | lease_agreement										1									1	1	1	1	1
Five Star
Concentration Risk [Line Items]
Number of Communities Included in Expansion and Development Project												2
Related Party Transaction, Annual Rent Increase Percentage In Addition to Rate Applicable on Outstanding Borrowings												2.00%
Revenues | $																				$ 210,539
Total rental income recognized | $																								203,581	196,919
Rents receivable | $				$ 18,320	$ 18,320					$ 18,539				$ 18,320					$ 18,539	$ 18,539	$ 18,539	$ 18,539	$ 18,539	18,320
Number of units that may be re-assigned to an existing or to a new long term lease										1									1	1	1	1	1
Real estate improvements by lessee purchased | $																				$ 39,800				21,438	21,444
Increase (decrease) in annual lease rent payable | $									$ 39											$ 3,193				1,719	1,734
Number of communities associated with leases in default					5
Number of pre-existing management agreements | lease_agreement						4
Number of pre-existing management agreements terminated | pooling_agreement						3
Minimum percentage of ownership of lessee's voting stock above which the entity has the option to cancel all its rights										9.80%									9.80%	9.80%	9.80%	9.80%	9.80%
Expenses from property management agreement transactions with related party | $																				$ 14,080				$ 11,918	$ 10,728
Five Star | Senior Living Communities
Concentration Risk [Line Items]
Number of consecutive renewal terms of agreement																						2	2
Property management agreement renewal period																			15 years
Number of communities managed																					70			68	60
Number of pre-existing management agreements | pooling_agreement		4
Number of management agreements		10
Number of pre-existing management agreements terminated | pooling_agreement		3
Number of separate management agreements entered for communities acquired | pooling_agreement						10
Property management agreement, number of communities subject to reset of annual minimum return | agreement		10
Number of agreements with related party to provide management services to entity | lease_agreement																						2
Expenses from property management agreement transactions with related party | $																				$ 7,525				$ 7,707	$ 7,737
A L Pooling Agreements | Five Star
Concentration Risk [Line Items]
Related Party Transaction, Annual Rent Increase Percentage In Addition to Rate Applicable on Outstanding Borrowings	2.00%											2.00%
Number of consecutive renewal terms of agreement		8	2
Property management agreement renewal period		5 years	15 years
Management fees as a percentage of gross revenues	5.00%
Incentive fee as a percentage of annual net operating income after realization of specified percentage of annual return	20.00%
Property management agreement, annual return as a percentage of invested capital	7.00%	7.00%
Property management agreement, payment of capital expenditure as percentage of the funded amount	3.00%	3.00%								7.00%									7.00%	7.00%	7.00%	7.00%	7.00%
Incentive fee payable | $		$ 0
Minimum | Five Star | Senior Living Communities
Concentration Risk [Line Items]
Property management agreement renewal period																			10 years
Minimum | A L Pooling Agreements | Five Star
Concentration Risk [Line Items]
Management fees as a percentage of gross revenues		3.00%								3.00%									3.00%	3.00%	3.00%	3.00%	3.00%
Incentive fee as a percentage of annual net operating income after realization of specified percentage of annual return		20.00%								20.00%									20.00%	20.00%	20.00%	20.00%	20.00%
Property management agreement, annual return as a percentage of invested capital										7.00%									7.00%	7.00%	7.00%	7.00%	7.00%
Maximum | Five Star | Senior Living Communities
Concentration Risk [Line Items]
Property management agreement renewal period																			15 years
Maximum | A L Pooling Agreements | Five Star
Concentration Risk [Line Items]
Management fees as a percentage of gross revenues		5.00%								5.00%									5.00%	5.00%	5.00%	5.00%	5.00%
Incentive fee as a percentage of annual net operating income after realization of specified percentage of annual return		35.00%								35.00%									35.00%	35.00%	35.00%	35.00%	35.00%
Property management agreement, annual return as a percentage of invested capital										8.00%									8.00%	8.00%	8.00%	8.00%	8.00%
Georgia | Five Star | Senior Living Communities
Concentration Risk [Line Items]
Number of communities associated with leases in default				395	5
California
Concentration Risk [Line Items]
Number of communities not included in pooling agreement																					1
NEW YORK
Concentration Risk [Line Items]
Number of communities owned and managed by related party | living_unit										310									310	310	310	310	310
Management fees as a percentage of gross revenues										5.00%									5.00%	5.00%	5.00%	5.00%	5.00%
Incentive fee payable | $										$ 0									$ 0	$ 0	$ 0	$ 0	$ 0
Five Star
Concentration Risk [Line Items]
Number of communities leased by the company				185	185					185				185					185	185	185	185	185	185	177
Number of leases with related party | lease_agreement																						5
Annual rent as a percentage of gross revenues, percent										4.00%									4.00%	4.00%	4.00%	4.00%	4.00%
Annual rent as a percentage of gross revenues, amount | $																				$ 5,533				$ 5,686	$ 5,666
Related party transaction, annual rents due | $																				206,329
Five Star | Lease No. 1
Concentration Risk [Line Items]
Number of communities																					83
Five Star | Lease No. 2
Concentration Risk [Line Items]
Number of communities																					47
Five Star | Lease No. 3
Concentration Risk [Line Items]
Number of communities																					17
Five Star | Lease No. 4
Concentration Risk [Line Items]
Number of communities																					29
Five Star | Lease No. 5
Concentration Risk [Line Items]
Number of communities																					9
Acquisitions | Senior Living Communities
Concentration Risk [Line Items]
Number of communities							1
Acquisitions | Five Star | Senior Living Communities
Concentration Risk [Line Items]
Number of communities								1
Number of communities managed																					5
Number of communities owned and managed by related party acquired during the period | property	6
Number of management agreements | pooling_agreement			2
Acquisitions | Alabama and Indiana | Five Star | Senior Living Communities
Concentration Risk [Line Items]
Number of communities owned and managed by related party acquired during the period | property	2
Rents from significant lessee | Sales Revenue, Services, Net
Concentration Risk [Line Items]
Revenues | $																				1,074,819				1,058,022
Rents from significant lessee | Five Star | Sales Revenue, Services, Net
Concentration Risk [Line Items]
Revenues | $																				$ 210,539				$ 203,581