Related Party Transactions (Details) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended		1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Tel(x) [Member] sqft	Sep. 30, 2011 Tel(x) [Member]	Sep. 30, 2012 Tel(x) [Member] contract sqft	Sep. 30, 2011 Tel(x) [Member]	Dec. 31, 2011 Tel(x) [Member] contract sqft	Dec. 31, 2006 Tel(x) [Member] contract	Sep. 30, 2011 Unrelated Third Party [Member] contract sqft	Sep. 30, 2012 SoftLayer [Member]	Sep. 30, 2011 SoftLayer [Member]	Sep. 30, 2012 SoftLayer [Member] contract	Sep. 30, 2011 SoftLayer [Member]	Sep. 30, 2012 Minimum [Member] SoftLayer [Member]	Sep. 30, 2012 Maximum [Member] SoftLayer [Member]
Related Party Transaction [Line Items]
Number of leases agreement							43		41	10	2			9
Lease expiration, date							2026									2013	2025
Terms of lease extended through							2046
Rental revenues	$ 260,052,000	$ 206,846,000	$ 717,809,000	$ 606,447,000	$ 12,000,000	$ 11,400,000	$ 33,700,000	$ 30,900,000				$ 19,400,000	$ 4,700,000	$ 41,200,000	$ 11,600,000
Square footage of net rentable space					259,294		259,294		254,314		4,980
Percentage rent lease revenue earned					$ 1,700,000	$ 1,400,000	$ 3,100,000	$ 2,100,000
Percentage of rent for management fee							1.00%
Lease option extension date																2018	2035