Other Assets (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Other Assets
Deferred leasing costs	$ 15,019	$ 14,886
Deferred rent receivable	15,213	15,017
Deferred financing costs	4,303	2,520
Leasehold interests in corporate headquarters	4,151	4,152
Other	9,009	7,981
Total	47,695	44,556
Estimated amortization of deferred leasing costs
Remaining 2013	2,760
2014	3,332
2015	2,308
2016	1,702
2017	1,148
Thereafter	3,769
Total	$ 15,019	$ 14,886