Related Party Transactions (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 contract sqft	Dec. 31, 2011 contract sqft	Dec. 31, 2010	Dec. 31, 2006 contract
Related Party Transaction [Line Items]
Rental revenues	$ 990,715,000	$ 820,711,000	$ 682,026,000
Tel(x) [Member]
Related Party Transaction [Line Items]
Number of leases agreement	44	41		10
Lease expiration, date	2026
Terms of lease extended through	2046
Rental revenues	46,400,000	42,500,000	26,800,000
Square footage of net rentable space	288,940	254,314
Percentage rent lease revenue earned	4,800,000	3,600,000	2,500,000
Percentage of rent for management fee	1.00%
Unrelated Third Party [Member]
Related Party Transaction [Line Items]
Number of leases agreement	3
Square footage of net rentable space	34,626
SoftLayer [Member]
Related Party Transaction [Line Items]
Number of leases agreement	9
Rental revenues	$ 48,300,000	$ 20,200,000	$ 4,200,000
Minimum [Member] | SoftLayer [Member]
Related Party Transaction [Line Items]
Lease expiration, date	2013
Lease option extension date	2018
Maximum [Member] | SoftLayer [Member]
Related Party Transaction [Line Items]
Lease expiration, date	2025
Lease option extension date	2035