Intangible Assets and Liabilities - Annual Amortization of Intangible Assets, Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets
2018 (three months remaining)	$ 3,645
2019	12,735
2020	10,140
2021	7,538
2022	5,355
Thereafter	15,726
Intangible Assets, net	55,139	$ 64,972
Liabilities
2018 (three months remaining)	844
2019	2,833
2020	2,069
2021	1,432
2022	1,264
Thereafter	9,238
Acquired Lease Intangibles, Net	$ 17,680	$ 20,274