Other Assets (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Assets
Lease inducements, net of accumulated amortization of $3,373 and $4,718 in 2013 and 2012, respectively	$ 9,743	$ 11,089
FF&E and leasehold improvements, net of accumulated depreciation of $19,070 and $18,877 in 2013 and 2012, respectively	6,894	4,814
Prepaid Expense and Other Assets, Current	3,476	2,044
Predevelopment costs and earnest money	2,765	3,284
Loan closing costs, net of accumulated amortization of $2,285 and $2,624 in 2013 and 2012, respectively	4,379	3,704
Intangible Assets:
In-place leases, net of accumulated amortization of $7,640 and $5,729 in 2013 and 2012, respectively	162,792	21,637
Above market leases, net of accumulated amortization of $9,727 and $9,424 in 2013 and 2012, respectively	12,988	6,892
Finite Lived Intangible Asset Below Market Ground Leases Net	1,701	0
Goodwill	4,147	4,751	5,155
Total Other Assets	208,885	58,215
Accumulated amortization, incentives to lessees	3,892	4,718
Accumulated depreciation on FF&E and leasehold improvements	19,755	18,877
Accumulated amortization on loan closing costs	2,784	2,624
Accumulated amortization of in place leases	16,276	5,729
Accumulated amortization of finite-lived intangible assets, above market leases	10,629	9,424
Accumulated Amortization of Finite Lived Intangible Assets Below Market Ground Leases	$ 24	$ 0