Related Party Transactions (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Tel(x) [Member] sqft	Jun. 30, 2011 Tel(x) [Member]	Jun. 30, 2012 Tel(x) [Member] contract sqft	Jun. 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	Jun. 30, 2012 SoftLayer [Member]	Jun. 30, 2011 SoftLayer [Member]	Jun. 30, 2012 SoftLayer [Member] contract	Jun. 30, 2011 SoftLayer [Member]	Jun. 30, 2012 Minimum [Member] SoftLayer [Member]	Jun. 30, 2012 Maximum [Member] SoftLayer [Member]
Related Party Transaction [Line Items]
Number of leases agreement										10	2			9
Lease expiration, date			2026													2013	2025
Terms of lease extended through			2046
Rental revenues	$ 234,923,000	$ 202,806,000	$ 457,757,000	$ 399,601,000	$ 11,300,000	$ 10,700,000	$ 21,700,000	$ 19,500,000				$ 14,500,000	$ 4,600,000	$ 21,700,000	$ 6,900,000
Square footage of net rentable space					259,294		259,294		254,314		4,980
Lease agreements							43		41
Percentage rent lease revenue earned					$ 1,100,000	$ 600,000	$ 1,400,000	$ 700,000
Percentage of rent for management fee			1.00%
Lease option extension date																2018	2035