Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Related Party Transactions
Rental revenue	$ 131,080	$ 116,146	$ 101,449
Affiliate of the Carlyle Group | VA1- Mortgage loan
Related Party Transactions
Net rentable space leased to an affiliate (in square feet)	1,520
Common interest (as a percent)	54.60%
Rental revenue	$ 400	$ 300	$ 200
Affiliate of the Carlyle Group | LA1, Los Angeles, CA
Related Party Transactions
Net rentable space leased to an affiliate (in square feet)	375