Investment in Real Estate (Details) (USD $)	6 Months Ended						6 Months Ended				0 Months Ended			6 Months Ended
	Jun. 30, 2013 item	Dec. 31, 2012	Jun. 30, 2013 SV1, San Jose, CA	Jun. 30, 2013 SV2, Milpitas, CA	Jun. 30, 2013 SV3, Santa Clara, CA	Jun. 30, 2013 SV4, Santa Clara, CA	Jun. 30, 2013 SV5, Santa Clara, CA	Jun. 30, 2013 Santa Clara Campus, Santa Clara, CA	Jun. 30, 2013 BO1, Somerville, MA	Jun. 30, 2013 NY1, New York, NY	Feb. 07, 2013 NY2, Secaucus, NJ	Jun. 30, 2013 NY2, Secaucus, NJ	Jun. 30, 2013 VA1, Reston, VA	Jun. 30, 2013 VA2, Reston, VA	Jun. 30, 2013 DC1, Washington, DC	Jun. 30, 2013 CH1, Chicago, IL	Jun. 30, 2013 LA1, Los Angeles, CA	Jun. 30, 2013 LA2, Los Angeles, CA	Jun. 30, 2013 MI1, Miami, FL	Jun. 30, 2013 DE1, Denver, CO	Jun. 30, 2013 DE2, Denver, CO
Investment in Real Estate
Real estate value of acquired land and a vacant building											$ 23,000,000
Number of other data center facilities on which development is commenced	2
Reclassification of property							2,400,000							5,200,000
Land	76,227,000	85,868,000	6,863,000	5,086,000	3,972,000	4,442,000		8,173,000	6,100,000				6,903,000			5,493,000		28,467,000	728,000
Buildings and Improvements	652,142,000	596,405,000	103,090,000	23,270,000	45,820,000	84,746,000		8,221,000	77,354,000				104,650,000			74,594,000		120,579,000	9,818,000
Leasehold improvements	91,175,000	85,907,000								31,830,000					7,189,000		51,645,000			219,000	292,000
Construction in progress	104,963,000	61,328,000	14,098,000	431,000	18,000	490,000	14,771,000	4,969,000	2,219,000	404,000		44,279,000	4,162,000	9,765,000	218,000	5,297,000	1,712,000	1,245,000	24,000	486,000	375,000
Total investments in real estate	$ 924,507,000		$ 124,051,000	$ 28,787,000	$ 49,810,000	$ 89,678,000	$ 14,771,000	$ 21,363,000	$ 85,673,000	$ 32,234,000		$ 44,279,000	$ 115,715,000	$ 9,765,000	$ 7,407,000	$ 85,384,000	$ 53,357,000	$ 150,291,000	$ 10,570,000	$ 705,000	$ 667,000