Employee Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 1,307
Interest cost	3,021	3,259	3,474
Expected return on plan assets	(3,934)	(3,781)	(4,030)
Amortization of prior service cost	0	0	0
Amortization of losses (gains)	673	466	2,526
Net periodic benefit (credit) cost	(240)	(56)	3,277
Postretirement
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	6	4
Interest cost	38	53	42
Expected return on plan assets	0	0	0
Amortization of prior service cost	0	0	0
Amortization of losses (gains)	2	(1)	(13)
Net periodic benefit (credit) cost	$ 47	$ 58	$ 33