Deferred Revenue and Acquisition Related Liabilities, net Deferred Revenue and Acquisition Related Liabilities, net (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Deferred Revenue [Abstract]
Deferred revenue related to tenant-funded tenant improvements	$ 56,461		$ 41,884
Other deferred revenue	2,314		1,310
Acquisition-related intangible liabilities, net	59,129	[1],[2]	36,587	[1],[2]
Deferred revenue and acquisition-related intangible liabilities, net	117,904		79,781
2013	10,054
2014	9,339
2015	8,255
2016	7,825
2017	6,409
Thereafter	14,579
Total	$ 56,461

[1] See Note 4 for additional information.

[2] Included in deferred revenue and acquisition-related intangible liabilities, net in the consolidated balance sheets.