Related Person Transactions (Details) (USD $)	1 Months Ended	12 Months Ended		0 Months Ended		12 Months Ended			1 Months Ended	12 Months Ended												0 Months Ended			12 Months Ended	0 Months Ended	12 Months Ended		1 Months Ended	3 Months Ended	12 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended
	Jan. 31, 2013 property sqft	Dec. 31, 2013 sqft item	Dec. 31, 2012 sqft	Mar. 12, 2012 SIR	Feb. 16, 2012 SIR property sqft	Dec. 31, 2013 SIR	Dec. 31, 2012 SIR	Dec. 31, 2013 Maximum	Jul. 31, 2013 RMR item	Dec. 31, 2013 RMR office item sqft	Dec. 31, 2012 RMR	Dec. 31, 2011 RMR	Dec. 31, 2013 RMR SIR	Dec. 31, 2012 RMR SIR	Dec. 31, 2011 RMR SIR	Dec. 31, 2013 RMR Restricted shares	Dec. 31, 2012 RMR Restricted shares	Dec. 31, 2011 RMR Restricted shares	Dec. 31, 2013 RMR Maximum	Dec. 31, 2012 RMR Maximum	Dec. 31, 2011 RMR Maximum	Dec. 19, 2013 RMR Amended Agreement item	Dec. 31, 2013 RMR Amended Agreement Maximum	Dec. 19, 2013 RMR Amended Agreement Maximum	Dec. 31, 2013 RMR Australia	Mar. 15, 2013 GOV	Dec. 31, 2013 GOV	Dec. 31, 2009 GOV	Sep. 30, 2011 SNH property sqft	Jan. 31, 2011 SNH property	Dec. 31, 2013 SNH	Mar. 31, 2011 SNH sqft	Dec. 31, 2008 SNH Agreement to sell property	Jun. 30, 2013 AIC	Dec. 31, 2013 AIC item	Dec. 31, 2012 AIC	Dec. 31, 2011 AIC
Related person transactions
Number of employees		0
Number of agreements										2
Number of entities independent trustees serving as independent directors or independent trustees of other public companies to which related party provides management services										2
Base management fee payable as a percentage of average historical cost of real estate investments, up to specified amount																						0.70%
Threshold amount of real estate investments for payment of base management fee																			$ 250,000,000	$ 250,000,000	$ 250,000,000		$ 250,000,000
Base management fee payable as a percentage of average historical cost of real estate investments, located outside the United States, Puerto Rico and Canada										1.00%	1.00%	1.00%										1.00%
Base management fee payable as a percentage of average historical cost of real estate investments, exceeding specified amount																						0.50%
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																								250,000,000
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																						250,000,000
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%
Measurement period of incentive management fee																						3 years
Portion of shares issued in payment of an incentive management fee																						33.00%
Portion of remaining shares to be vested in equal annual installments																						67.00%
Number of equal annual installments for vesting of common shares																						2
Number of times registration right can be exercisable																						2
Base management fee payable as a percentage of average historical cost of real estate investments, located in the United States, Puerto Rico and Canada										0.70%	0.70%	0.70%
Annual business management fee as a percentage of aggregate cost of properties acquired in excess of $250,000										0.50%	0.50%	0.50%
Incentive fee as a percentage of the product of weighted average common shares outstanding on a fully diluted basis and the excess, if any of the Normalized FFO Per Share for current fiscal year over the preceding fiscal year										15.00%	15.00%	15.00%
Business management fees												39,203,000	43,279,000	43,646,000
Incentive fees paid										0	0	0
Property management fees as a percentage of gross collected rents										3.00%															3.00%
Construction supervision fees as a percentage of construction costs										5.00%															5.00%
Property management and construction supervision fees												30,315,000	32,460,000	33,689,000
Compensation for business management and real estate investment services as a percentage of average historical cost of CWHAT's real estate investments																									0.50%
Compensation for property management services as a percentage of difference between 3.0% of collected gross rents and the aggregate of all amounts paid or payable by or on behalf of CWHAT to third party property managers																									50.00%
Compensation for construction supervision services as a percentage of difference between 5.0% of constructions costs and any amounts paid to third parties for construction management and/or supervision																									50.00%
Business and property management fees																									1,626,000
Payments to MacarthurCook Fund Management Limited										161,000	1,814,000	1,856,000
Pro rata share of related party's costs of providing internal audit function													296,000	355,000	240,000
Successive renewal period for business and property management agreements										1 year
Period of prior written notice for termination of either agreement by entity or related party										60 days
Number of business days notice for termination of either agreement by related party, if entity undergoes a change of control										5 days
Number of regional offices leased										11
Rental income earned										828,000	564,000	566,000
Lease term										3 years
Square feet		37,273,000	61,806,000		21,400,000					32,500																			1,310,000			2,803,000
Number of shares granted under the Award Plan						2,000				73,450	71,617	73,050				73,450	71,617	73,050
Aggregate value of restricted shares granted (in dollars)										1,742,000	1,111,000	1,458,000
Vesting rights percentage for restricted shares vesting on the grant date										20.00%
Vesting rights percentage for restricted shares vesting on each of the next four anniversaries of the grant date										20.00%
Number of anniversaries of the grant date for vesting of restricted shares										4 years
Ownership percentage prior to transaction				100.00%		100.00%																					100.00%				100.00%
Minimum ownership of outstanding common shares of related party required to engage the same manager or common managing trustees																												10.00%			10.00%
Shares sold				9,200,000																						9,950,000
Net proceeds received on sale of common shares																										239,576,000
Realized gain on sale of common shares																										66,293,000
Amount of reimbursements payable to related party		9,385,000	12,958,000			636,000																					310,000
Shares owned by related party																															250,000
Less than wholly owned subsidiary, common shares owned						22,000,000	22,000,000
Less than wholly owned subsidiary, parent ownership interest percentage							56.00%
Proceeds from Issuance Initial Public Offering				180,814,000
Repayment of promissory note					400,000,000
Common shares consideration received on transfer of properties					22,000,000
Number of properties sold or transferred or agreed to be sold or transferred					79
Number of separate buildings or land parcels sold or transferred or agreed to be sold or transferred					251
Number of Properties Sold	3																												7	15			45
Number of maximum MOBs, in respect of which right of first refusal to purchase is granted																																	45
Number of buildings sold	18																												13	27
Aggregate sale price of properties sold, excluding closing costs																													167,000,000	470,000,000
Net gains on sale of properties		1,596,000																											7,846,000	168,272,000
Number of other companies which are shareholders of related party									2																										3
Equity method investments, ownership percentage						44.20%		50.00%																											12.50%
Amount invested in equity investee																																			5,209,000
Period for which property insurance program was purchased																																			1 year
Coverage amount for property insurance																																			500,000,000
Premium for property insurance																																		5,984,000		6,560,000	6,697,000
Aggregate non-indemnifiable coverage of combined directors' and officers' liability insurance policy purchased by the entity									10,000,000
Aggregate excess coverage of combined directors' and officers' liability insurance policy purchased									5,000,000
Premium paid for combined directors' and officers' liability insurance policy									133,000
Legal fees and costs										$ 30,392,000