Employee Benefit Plans - Net Periodic Benefit Pension Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of net periodic benefit cost
Interest cost	$ 2,031	$ 1,712	$ 1,635
Expected return on plan assets	(3,820)	(3,802)	(4,057)
Recognized net actuarial loss	533	591	571
Amortization of prior service cost	0	0	0
Recognized settlement loss	2,703	2,480	1,338
Net periodic cost (income)	1,447	981	(513)
Other changes in plan assets and benefit obligations recognized as a charge to other comprehensive (loss) income
Net loss for the period	(7,086)	(83)	(3,911)
Amortization of net loss	3,236	3,071	1,909
Total unrealized (loss) gain	(3,850)	2,988	(2,002)
Total recognized in net periodic pension cost and other comprehensive (loss) income	$ (5,297)	$ 2,007	$ (1,489)
Weighted-average assumptions used to determine the net periodic cost
Discount rate	3.45%	3.86%	3.99%
Expected return on plan assets	5.75%	6.25%	6.50%