Savings, Pension and Other Postretirement Employee Benefit Plans - Multiemployer Defined Benefit Plans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / h $ / Hour	Dec. 31, 2018 USD ($)	Dec. 31, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Multiemployer Defined Benefit Plans Contribution Rate | $ / Hour	4.0
Multiemployer Plans, Withdrawal Obligation	$ 81,600
Entity Tax Identification Number	516031295
Contributions (in thousands)	$ 5,600	$ 5,700	$ 6,100
IAM
Defined Benefit Plan Disclosure [Line Items]
Multiemployer Plan Number	002
Multiemployer Plans, Certified Zone Status [Fixed List]	Red	Green
Contributions (in thousands)	$ 270	$ 316	333
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	May 31, 2023
USW
Defined Benefit Plan Disclosure [Line Items]
Multiemployer Defined Benefit Plans Contribution Rate | $ / h	2.79
Entity Tax Identification Number	116166763
Multiemployer Plan Number	001
Multiemployer Plans, Certified Zone Status [Fixed List]	Red	Red
Contributions (in thousands)	$ 5,331	$ 5,386	$ 5,815
Multiemployer Plans, Surcharge [Fixed List]	No
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date	Aug. 31, 2017
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	6.80%
defined benefit plan, ultimate health care cost trend rates, with added benefits	4.50%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.90%
Maximum | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
defined benefit plan, ultimate health care cost trend rates, with added benefits	3.80%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	3.80%