Related Person Transactions (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			1 Months Ended				12 Months Ended				12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended		0 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2014 RMR item	Jul. 31, 2013 RMR item	Jun. 30, 2011 RMR item	May 31, 2011 RMR item	Dec. 31, 2013 RMR director	Dec. 31, 2012 RMR	Dec. 31, 2011 RMR	Jun. 30, 2014 RMR Subsequent event item	Dec. 31, 2013 RMR Share Award Plans Restricted shares	Dec. 31, 2012 RMR Share Award Plans Restricted shares	Dec. 31, 2011 RMR Share Award Plans Restricted shares	Jun. 30, 2013 AIC	Dec. 31, 2013 AIC item	Dec. 31, 2012 AIC	Dec. 31, 2011 AIC	Jun. 30, 2014 AIC Subsequent event	May 09, 2014 AIC Subsequent event item	May 09, 2014 AIC CWH Subsequent event	Dec. 31, 2013 AIC Maximum	Dec. 31, 2013 Messrs. Mackey, Hoagland and Larkin
Related person transactions
Number of Managing Directors also serving as Chairman, majority owner and an employee								1
Minimum percentage of business time devoted for services																							80.00%
Percentage of total cash compensation paid								80.00%
Management fees receivable under property management agreement as a percentage of gross revenues								0.60%
Business management fees								$ 13,965	$ 13,226	$ 11,823
share in cost of providing internal audit function								203	209	247
Renewal period								1 year
Period before which a written notice is required to be given for termination of the service agreement								60 days
Period before which a notice is required for termination of the business management agreement upon change in control								5 days
Number of buildings owned						2	1
Annual rent expense under leases								767
Utilities and real estate taxes	193,820	190,184	183,950					1,386	1,426	1,271
Awards granted (in shares)												82,000	81,000	77,000
Aggregate value of awards granted during the period												373	399	168
Portion of the awards granted that vested on the grant date (as a percent)												20.00%
Portion of the awards granted, which will vest on each of the next four anniversaries of the grant date (as percent)												20.00%
Number of anniversaries of the grant date over which the awards vest												4 years
Ownership percentage																12.50%				14.30%		20.00%
Number of other current shareholders of the related party																5
Amount invested in equity investee																5,209
Equity investment in Affiliates Insurance Company	5,913	5,629														5,913	5,629
Income (loss) arising from investment	334	316	139													334	316	139
Period for which property insurance coverage															1 year
Coverage of property insurance															500,000
Annual premiums															5,428		6,264	4,500	3,901
Number of entities to whom RMR provides management services											3
Shares issued by related party																					3
Value of shares issued by related party																					825
Aggregate coverage of combined directors' and officers' liability insurance policy purchased by the related party				10,000	10,000
Aggregate excess layer coverage of combined directors' and officers' liability insurance policy purchased by the related party				20,000	5,000
Premium paid for combined directors' and officers' liability insurance policy				357	133
Remaining share holders holds the percentage																				6
Period for which directors' and officers' insurance coverage				2 years
Number of entities to whom RMR manages				4	4
Period for which additional directors' and officers' insurance coverage				1 year
Aggregate excess non-indemnifiable coverage of combined directors' and officers' liability insurance policy purchased by the related party				$ 5,000