Intangible Assets and Liabilities - Annual Amortization of Intangible Assets, Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets
2018 (six months remaining)	$ 7,539
2019	13,021
2020	10,353
2021	7,538
2022	5,355
Thereafter	15,612
Intangible Assets, net	59,418	$ 64,972
Liabilities
2018 (six months remaining)	1,736
2019	2,833
2020	2,069
2021	1,432
2022	1,264
Thereafter	9,239
Acquired Lease Intangibles, Net	$ 18,573	$ 20,274