Intangible Assets and Liabilities Estimated Future Annual Amortization Expense (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Intangible Assets [Abstract]
2019 (amount remaining at March 31, 2019)	$ 54,492
2020	52,891
2021	37,209
2022	27,015
2023	19,366
Beyond 2023	46,115
Total intangible assets subject to amortization (accretion)	237,088	$ 254,483
2019 (amount remaining at March 31, 2019)	(6,175)
2020	(8,028)
2021	(1,963)
2022	(459)
2023	0
Beyond 2023	0
Intangible liabilities, Net	(16,625)	$ (18,683)
2019 (amount remaining at March 31, 2019)	48,317
2020	44,863
2021	35,246
2022	26,556
2023	19,366
Beyond 2023	46,115
Total intangible assets (liabilities), net	$ 220,463