Basis of presentation (Details 2)	9 Months Ended
Sep. 30, 2012	Dec. 31, 2011
Basis of presentation
Maximum period within which sale of property is expected to be completed	1 year
Investments
Ownership interest percentage in the voting stock of each individual privately held entity	10.00%	10.00%

The percentage of ownership of common stock, less than ten percent in the investee accounted for under the cost method of accounting.

No definition available.

Name:	are_CostMethodInvestmentOwnershipPercentage
Namespace Prefix:	are_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant