Employee Benefit Plans - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) participant	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Cost recognized	$ 1,488	$ 1,299	$ 1,097
Effect of one percentage point increase in assumed health care costs, affect on accumulated benefit obligation	69
Effect of one percentage point decrease in assumed health care costs, effect on accumulated benefit obligation	(104)
Effect of one percentage point increase in assumed health care costs, affect on service and interest cost	4
Effect of one percentage point decrease in assumed health care costs, affect on service and interest cost	$ (3)
Post-employment benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of participants | participant	181
Number of active participants eligible for benefits | participant	25
Minimum age of participant to become eligible for benefits	62 years
Requisite service period	5 years
Age up to which health benefits continuation paid	65 years
Expected contributions in next fiscal year, before Medicare Part D subsidy receipts	$ 484
Medicare Part D subsidy receipts to the plan in next fiscal year	484
Expected contributions in next fiscal year, net of Medicare Part D subsidy receipts	467
Post-employment benefits | Medicare Part D Subsidy Receipts
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Medicare Part D subsidy receipts to the plan in next fiscal year	$ 17