Postretirement Benefits Other Than Pensions - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service costs, before tax	$ 2,200	$ 2,600
Unrecognized prior service costs, net of tax	1,700	1,600
Unrecognized actuarial gains (losses), before tax	(128,200)	(122,100)
Unrecognized actuarial gains (losses), net of tax	(96,300)	(74,400)
Prior service costs expected to be recognized next fiscal year	400
Prior service costs expected to be recognized next fiscal year, net of tax	300
Actuarial losses expected to be recognized next fiscal year	(9,800)
Actuarial losses expected to be recognized next fiscal year, net of tax	(7,200)
Accrued postretirement liability, current	2,400
Employer expected contribution	2,400
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service costs, before tax	300	400
Unrecognized prior service costs, net of tax	200	300
Unrecognized actuarial gains (losses), before tax	6,100	4,600
Unrecognized actuarial gains (losses), net of tax	4,600	3,400
Prior service costs expected to be recognized next fiscal year	100
Prior service costs expected to be recognized next fiscal year, net of tax	100
Actuarial losses expected to be recognized next fiscal year	600
Actuarial losses expected to be recognized next fiscal year, net of tax	500
Unfunded portion of the liability	$ 29,914	$ 31,866