Leases and Management Agreements with Five Star (Details)		1 Months Ended					3 Months Ended								5 Months Ended	12 Months Ended
	Jun. 29, 2016 USD ($) community lease_agreement pooling_agreement	Dec. 31, 2016 USD ($) living_unit community lease_agreement management_agreement	Jun. 30, 2016 lease_agreement pooling_agreement	May 31, 2016 living_unit community	Dec. 31, 2015 USD ($) community	Feb. 28, 2015 USD ($)	Dec. 31, 2016 USD ($) living_unit community	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) community	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2015 community	Dec. 31, 2016 USD ($) living_unit community	Dec. 31, 2016 USD ($) living_unit community	Dec. 31, 2016 USD ($) living_unit community	Dec. 31, 2016 USD ($) living_unit community	Dec. 31, 2016 USD ($) living_unit community lease_agreement	Dec. 31, 2016 USD ($) living_unit community	Dec. 31, 2016 USD ($) living_unit community management_agreement	Dec. 31, 2016 USD ($) living_unit community customer	Dec. 31, 2015 USD ($) community	Dec. 31, 2014 USD ($) community	May 31, 2015
Concentration of Credit Risk.
Real estate improvements by lessee purchased | $																		$ 21,438,000						$ 21,444,000
Real estate property, gross | $		$ 7,730,523,000			$ 7,456,940,000		$ 7,730,523,000				$ 7,456,940,000					$ 7,730,523,000	$ 7,730,523,000	7,730,523,000	$ 7,730,523,000	$ 7,730,523,000	$ 7,730,523,000	$ 7,730,523,000	$ 7,730,523,000	7,456,940,000
Total revenues | $							274,296,000	$ 263,983,000	$ 261,367,000	$ 258,375,000	267,519,000	$ 255,275,000	$ 247,402,000	$ 228,577,000				1,058,022,000						$ 998,773,000	$ 844,887,000
Number of third parties in default | customer																							1
Property management agreement, number of communities subject to reset of annual minimum return | community	10
Senior Living Communities
Concentration of Credit Risk.
Number of communities | community															19
Sales Revenue, Services, Net | Rents from significant lessee
Concentration of Credit Risk.
Concentration of credit risk (as a percent)																					100.00%			100.00%
Total revenues | $																		1,058,022,000						$ 998,773,000
Sales Revenue, Services, Net | Rents from significant lessee | Other Customers
Concentration of Credit Risk.
Concentration of credit risk (as a percent)																					81.00%			80.00%
Total revenues | $																		854,441,000						$ 801,854,000
Sales Revenue, Services, Net | Rents from significant lessee | Five Star
Concentration of Credit Risk.
Concentration of credit risk (as a percent)																					19.00%			20.00%
Total revenues | $																		203,581,000						$ 196,919,000
Real Estate Investment Property At Cost | Rents from significant lessee
Concentration of Credit Risk.
Real estate property, gross | $		7,730,523,000			7,456,940,000		7,730,523,000				7,456,940,000					7,730,523,000	7,730,523,000	7,730,523,000	7,730,523,000	7,730,523,000	$ 7,730,523,000	7,730,523,000	$ 7,730,523,000	$ 7,456,940,000
Concentration of credit risk (as a percent)																					100.00%			100.00%
Real Estate Investment Property At Cost | Rents from significant lessee | Other Customers
Concentration of Credit Risk.
Real estate property, gross | $		5,437,266,000			5,309,552,000		5,437,266,000				5,309,552,000					5,437,266,000	5,437,266,000	5,437,266,000	5,437,266,000	5,437,266,000	$ 5,437,266,000	5,437,266,000	5,437,266,000	$ 5,309,552,000
Concentration of credit risk (as a percent)																					70.00%			71.00%
Real Estate Investment Property At Cost | Rents from significant lessee | Five Star
Concentration of Credit Risk.
Real estate property, gross | $		2,293,257,000			2,147,388,000		2,293,257,000				2,147,388,000					2,293,257,000	2,293,257,000	2,293,257,000	2,293,257,000	2,293,257,000	$ 2,293,257,000	2,293,257,000	2,293,257,000	$ 2,147,388,000
Concentration of credit risk (as a percent)																					30.00%			29.00%
Five Star
Concentration of Credit Risk.
Total rental income recognized | $																		203,581,000						$ 196,919,000	196,269,000
Rents receivable | $		$ 18,320,000			17,466,000		$ 18,320,000				$ 17,466,000					$ 18,320,000	$ 18,320,000	$ 18,320,000	$ 18,320,000	$ 18,320,000	$ 18,320,000	$ 18,320,000	$ 18,320,000	17,466,000
Number of units that may be re-assigned to an existing or to a new long term lease | community		1					1									1	1	1	1	1	1	1	1
Real estate improvements by lessee purchased | $																		$ 21,438,000						21,444,000	25,804,000
Increase or decrease in annual lease rent payable | $						$ 39,000												$ 1,719,000						1,734,000	2,066,000
Number of communities associated with leases in default | community		5
Number of pre-existing management agreements terminated | pooling_agreement			3
Number of pre-existing management agreements | lease_agreement		1	4
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%	9.80%	9.80%	9.80%	9.80%
Expenses from property management agreement transactions with related party | $																		$ 11,918,000						$ 10,728,000	$ 9,765,000
Five Star | Senior Living Communities
Concentration of Credit Risk.
Number of consecutive renewal terms of agreement																				2		2
Property management agreement renewal period																15 years
Increase or decrease in annual lease rent payable | $					$ (2,000)
Number of communities managed | community																			68					60	46
Number of communities owned and managed by related party | community		68					68									68	68	68	68	68	68	68	68
Number of communities owned and managed by related party acquired during the period | community																			8
Number of units within owned and managed by related party community | living_unit																	696
Number of pre-existing management agreements terminated | pooling_agreement	3
Number of pre-existing management agreements | pooling_agreement	4
Number of separate management agreements entered for communities acquired | pooling_agreement	10		10
Number of properties acquired, referred to as managed properties | living_unit																	68
Number of agreements with related party to provide management services to entity | lease_agreement																				2
A L Pooling Agreements | Five Star
Concentration of Credit Risk.
Number of consecutive renewal terms of agreement | lease_agreement	9
Property management agreement renewal period	5 years
Management fees as a percentage of gross revenues	5.00%																									3.00%
Incentive fee as a percentage of annual net operating income after realization of specified percentage of annual return	20.00%																									35.00%
Property management agreement, payment of capital expenditure as percentage of the funded amount	0.03
Incentive fee payable | $	$ 0
A L Pooling Agreements | Five Star | Senior Living Communities
Concentration of Credit Risk.
Property management agreement, number of communities subject to reset of annual minimum return | community	10
Property management agreement, annual return as a percentage of invested capital	7.00%
Minimum | Five Star | Senior Living Communities
Concentration of Credit Risk.
Property management agreement renewal period																10 years
Minimum | A L Pooling Agreements | Five Star
Concentration of Credit Risk.
Property management agreement, annual return as a percentage of invested capital																										8.00%
Maximum | Five Star | Senior Living Communities
Concentration of Credit Risk.
Property management agreement renewal period																15 years
Maximum | A L Pooling Agreements | Five Star
Concentration of Credit Risk.
Property management agreement, annual return as a percentage of invested capital	7.00%
Five Star
Concentration of Credit Risk.
Number of communities leased by the company | community		185			177		185				177					185	185	185	185	185	185	185	185	177	181
Number of leases with related party | lease_agreement																				5
Annual rent as a percentage of gross revenues, percent		0.04					0.04									0.04	0.04	0.04	0.04	0.04	0.04	0.04	0.04
Annual rent as a percentage of gross revenues, amount | $																		$ 5,686,000						$ 5,666,000	$ 5,752,000
Related party transaction, annual rents due | $																		$ 203,356,000
Five Star | Lease No. 1
Concentration of Credit Risk.
Number of communities | community																			83
Five Star | Lease No. 2
Concentration of Credit Risk.
Number of communities | community																			47
Five Star | Lease No. 3
Concentration of Credit Risk.
Number of communities | community																			17
Five Star | Lease No. 4
Concentration of Credit Risk.
Number of communities | community																			29
Five Star | Lease No. 5
Concentration of Credit Risk.
Number of communities | community																			9
North Carolina and Alabama | Five Star | Senior Living Communities
Concentration of Credit Risk.
Number of communities owned and managed by related party acquired during the period | community																			2
Number of units within owned and managed by related party community | living_unit																	263
Georgia | Five Star | Senior Living Communities
Concentration of Credit Risk.
Number of communities managed | community		5
Number of communities owned and managed by related party acquired during the period | community				1
Number of units within owned and managed by related party community | living_unit				38
Number of units within communities associated with leases in default | living_unit																	395
Number of communities associated with leases in default | community																			5
Number of management agreements added to pooling agreements | management_agreement		4
Number of management agreements added to pre-existing management agreements | management_agreement		1
California
Concentration of Credit Risk.
Number of communities not included in pooling agreement | community																			1
NEW YORK
Concentration of Credit Risk.
Number of communities owned and managed by related party | living_unit		310					310									310	310	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%	5.00%	5.00%	5.00%	5.00%
Incentive fee payable | $		$ 0					$ 0									$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0