Employee Benefit Plans - Pension Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net periodic benefit cost
Service cost	$ 80	$ 82
Interest cost	2,448	2,350
Employer contributions	2,557	2,477
Pension And Postretirement [Member]
Net periodic benefit cost
Service cost	80	82	$ 8
Interest cost	2,448	2,350	2,288
Expected return on plan assets	(2,460)	(2,841)	(2,392)
Amortization of prior service cost	(169)	9	(134)
Amortization of net (gain) loss	1,768	1,755	2,063
Net periodic benefit cost	$ 1,667	$ 1,355	$ 1,833