Acquired Intangible Assets (Details) - Period Ending (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Intangible Assets, Net	$ 32,154	$ 20,957
Acquired Intangible Assets, Accumulated Amortization	5,584	3,844
Leases, Acquired-in-Place [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Intangible Assets, Net	23,288	15,655
Acquired Intangible Assets, Accumulated Amortization	3,575	2,310
Leases, Acquired-in-Place, Market Adjustment [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Intangible Assets, Net	8,866	5,302
Acquired Intangible Assets, Accumulated Amortization	$ 2,009	$ 1,534