Investment in Real Estate (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Investment in Real Estate
Land	$ 85,868	$ 84,738
Buildings and Improvements	593,020	499,717
Leasehold improvements	85,907	81,057
Construction in progress	61,328	73,084
Total investments in real estate	826,123
SV1, San Jose, CA
Investment in Real Estate
Land	6,863
Buildings and Improvements	102,390
Construction in progress	4,352
Total investments in real estate	113,605
SV2, Milpitas, CA
Investment in Real Estate
Land	5,086
Buildings and Improvements	22,086
Construction in progress	462
Total investments in real estate	27,634
SV3, Santa Clara, CA
Investment in Real Estate
Land	3,972
Buildings and Improvements	45,196
Construction in progress	17
Total investments in real estate	49,185
SV4, Santa Clara, CA
Investment in Real Estate
Land	4,442
Buildings and Improvements	55,800
Construction in progress	27,836
Total investments in real estate	88,078
Santa Clara Campus, Santa Clara, CA
Investment in Real Estate
Land	12,617
Buildings and Improvements	11,553
Construction in progress	1,775
Total investments in real estate	25,945
BO1, Somerville, MA
Investment in Real Estate
Land	6,100
Buildings and Improvements	68,337
Construction in progress	2,063
Total investments in real estate	76,500
NY1, New York, NY
Investment in Real Estate
Leasehold improvements	31,069
Construction in progress	223
Total investments in real estate	31,292
VA1, Reston, VA
Investment in Real Estate
Land	12,100
Buildings and Improvements	102,366
Construction in progress	5,356
Total investments in real estate	119,822
DC1, Washington, DC
Investment in Real Estate
Leasehold improvements	6,341
Construction in progress	452
Total investments in real estate	6,793
CH1, Chicago, IL
Investment in Real Estate
Land	5,493
Buildings and Improvements	68,138
Construction in progress	7,305
Total investments in real estate	80,936
LA1, Los Angeles, CA
Investment in Real Estate
Leasehold improvements	48,345
Construction in progress	3,489
Total investments in real estate	51,834
LA2, Los Angeles, CA
Investment in Real Estate
Land	28,467
Buildings and Improvements	107,488
Construction in progress	7,781
Total investments in real estate	143,736
MI1, Miami, FL
Investment in Real Estate
Land	728
Buildings and Improvements	9,666
Construction in progress	91
Total investments in real estate	10,485
DE1, Denver, CO
Investment in Real Estate
Leasehold improvements	143
Construction in progress	126
Total investments in real estate	269
DE2, Denver, CO
Investment in Real Estate
Leasehold improvements	9
Total investments in real estate	$ 9