Leases - Future Minimum Rental Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating lease rental income for leased assets
Operating lease rental income recognized	$ 7,800	$ 8,300	$ 9,700
Future minimum rental income under noncancelable operating leases with terms in excess of one year
2019	5,815
2020	5,811
2021	5,735
2022	4,721
2023	3,188
Thereafter	8,527
Total	$ 33,797