Segment Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 property sqft	Dec. 31, 2012 sqft	Dec. 31, 2011	Sep. 30, 2012 sqft
Segment information
Number of reportable segments	2
Number of geographical regions comprised mainly by properties owned by SIR	1
Number of remaining geographical regions	2
Square feet	37,273,000	61,806,000
Rental income	$ 707,380	$ 709,390	$ 601,632
Tenant reimbursements and other income	178,156	172,515	139,712
NOI	514,667	525,301	443,936
Investment in properties, net of accumulated depreciation	4,642,106	6,821,803
Minimum
Segment information
Percentage of CBD and suburban properties that are office properties	90.00%
CBD Properties
Segment information
Number of Real Estate Properties	38
Number of buildings	51
Square feet	20,975,000	21,224,000		20,166,000
Rental income	432,812	408,144	320,564
Tenant reimbursements and other income	118,314	112,083	79,277
NOI	291,544	280,036	221,737
Investment in properties, net of accumulated depreciation	3,001,397	3,176,446
CBD Properties | Australia
Segment information
Investment in properties, net of accumulated depreciation	141,966	168,220
Suburban Properties
Segment information
Number of Real Estate Properties	87
Number of buildings	144
Square feet	16,298,000	40,582,000		41,567,000
Rental income	274,568	301,246	281,068
Tenant reimbursements and other income	59,842	60,432	60,435
NOI	223,123	245,265	222,199
Investment in properties, net of accumulated depreciation	1,640,709	3,645,357
Suburban Properties | Australia
Segment information
Investment in properties, net of accumulated depreciation	$ 88,935	$ 104,010