Related Person Transactions (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended						1 Months Ended			12 Months Ended														0 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended
	Jul. 31, 2013 item	Dec. 31, 2013 sqft	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Share Award Plan	Dec. 31, 2012 Share Award Plan	Dec. 31, 2011 Share Award Plan	Jul. 31, 2013 RMR	Mar. 31, 2013 RMR	Mar. 31, 2012 RMR	Dec. 31, 2013 RMR item agreement	Dec. 31, 2012 RMR	Dec. 31, 2011 RMR	Dec. 31, 2013 RMR Office item sqft	Dec. 31, 2012 RMR Office	Dec. 31, 2011 RMR Office	Dec. 31, 2013 RMR Share Award Plan Officers and employees	Dec. 31, 2012 RMR Share Award Plan Officers and employees	Dec. 31, 2011 RMR Share Award Plan Officers and employees	Dec. 31, 2013 RMR Maximum	Dec. 31, 2012 RMR Maximum	Dec. 31, 2011 RMR Maximum	Dec. 23, 2013 RMR Amended Agreement item	Dec. 23, 2013 RMR Amended Agreement Maximum	Mar. 15, 2013 CWH	Dec. 31, 2013 CWH	Dec. 31, 2013 CWH Minimum	Jun. 30, 2013 AIC	Dec. 31, 2013 AIC item	Dec. 31, 2012 AIC	Dec. 31, 2011 AIC	Dec. 31, 2013 AIC Maximum
Related Party Transaction
Number of employees											0
Number of agreements to avail management and administrative services											2
Base management fee payable as a percentage of aggregate book value of real estate assets or transferred assets											0.50%	0.50%	0.50%										0.50%
Base management fee payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments up to specified amount											0.70%	0.70%	0.70%										0.70%
Threshold amount of real estate investments for payment of base management fee																				$ 250,000	$ 250,000	$ 250,000		$ 250,000
Base management fee payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments exceeding specified amount																							0.50%
Threshold amount of other real estate investments for payment of base management fee																							250,000
Base management fee payable as a percentage of average closing price per share of common shares on NYSE																							0.70%
Base management fee payable, average market capitalization																								250,000
Base management fee payable as a percentage of average market capitalization exceeding specified amount																							0.50%
Threshold amount of average market capitalization for payment of base management fee																							250,000
Base business management fee payable in cash (as a percent)																							90.00%
Base business management fee payable in common shares (as a percent)																							10.00%
Incentive management fee payable (as a percent)																							12.00%
Portion of shares issued in payment of an incentive management fee																							33.33%
Portion of remaining shares to be vested in equal annual installments																							66.66%
Number of equal annual installments for vesting of common shares																							2
Number of times registration right can be exercisable																							2
Incentive fee as a percentage of product of weighted average diluted outstanding common shares and excess of FFO per share											15.00%	15.00%	15.00%
Business management fees											9,341	9,077	7,741
Number of shares issued for the incentive fee for services rendered									20,230	39,141
Incentive fee payable											0
Management fees payable under property management agreement as a percentage of gross rents											3.00%
Construction supervision fees payable under property management agreement as a percentage of construction costs											5.00%
Property management and construction supervision fees											7,877	7,018	6,321
Pro rata share of RMR's internal audit costs											203	193	240
Period by which business management agreement and property management agreement get automatically renewed											1 year
Period before which the written notice is required to be given for cancellation of business management agreement and the property management agreement											60 days
Number of business days before which the notice is required to be given for termination of property management agreement											5 days
Rentable square feet of Properties		10,300,000												1,650
Number of regional offices leased														1
Rental income earned														31	32	31
Lease term														3 years
Awards granted (in shares)					58,350	93,058	50,850										48,350	43,917	40,850
Aggregate market value of shares awarded																	1,142	1,043	922
Restricted shares vesting terms																	0.20
Portion of the awards granted which will vest on each of the next four anniversaries of the grant date																	0.20
Number of anniversaries of the grant date over which the awards vest																	4 years
Percentage of interest in subsidiaries		100.00%																								100.00%
Percentage of interest																											10.00%		12.50%			20.00%
Shares sold by former parent company																									9,950,000
Common shares registration and sale expenses paid by related party																									310
Number of other companies owning interest in equity method investment																													5
Amount invested in equity investee																													5,194
Investment at carrying value																													6,031	5,747
Recognized income (loss) related to investment in AIC		334	316	139																									334	316	139
Program extension term																												1 year
Coverage of purchased property insurance																												500,000
Premium for property insurance																													1,161	410	1,286
Number of other companies to whom management services were provided by related party	4
Aggregate non-indemnifiable coverage of combined directors' and officers' liability insurance policy purchased by the related party								10,000
Aggregate coverage of combined directors' and officers' liability insurance policy purchased by the related party								5,000
Aggregate coverage of separate directors' and officers' liability insurance policy purchased								5,000
Premium paid for combined directors' and officers' liability insurance policy								$ 333