Postretirement Benefits Other Than Pensions - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service costs, before tax	$ 1,800	$ 2,200
Unrecognized prior service costs, net of tax	1,300	1,700
Unrecognized actuarial gains (losses), before tax	(112,300)	(128,200)
Unrecognized actuarial gains (losses), net of tax	(79,800)	(96,300)
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	(8,100)
Actuarial losses expected to be recognized next fiscal year, net of tax	(6,000)
Employer expected contribution	2,500
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service costs, before tax	200	300
Unrecognized prior service costs, net of tax	200	200
Unrecognized actuarial gains (losses), before tax	3,100	6,100
Unrecognized actuarial gains (losses), net of tax	2,300	4,600
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	$ 31,791	$ 29,914