Commitments and Contingencies - Narrative (Details) € in Millions					1 Months Ended		3 Months Ended				12 Months Ended		51 Months Ended
	Jun. 30, 2018 site	Nov. 07, 2017 USD ($)	Apr. 06, 2017 EUR (€)	Oct. 31, 2016 USD ($)	Oct. 31, 2019 USD ($)	Aug. 31, 2016 residence sampling_event	Mar. 31, 2020 USD ($) site mi	Dec. 31, 2019 USD ($) mi	Dec. 31, 2018 USD ($)	Dec. 31, 2015 USD ($) site	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) site	Mar. 31, 2020 USD ($) site mi	Jan. 24, 2020 USD ($)	Jan. 31, 2019 property	Jun. 30, 2016 EUR (€)	Mar. 31, 2016 USD ($)	Oct. 15, 2015 mine	Apr. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Feb. 19, 2014 site
Site Contingency [Line Items]
Number of sites subject to remediation | site							19						19
Number of sites, cost in excess of 100K | site							17						17
Cost per site minimis threshold							$ 100,000
Number of sites, discontinued operations | site							17						17
Number of sites, active operations | site							2						2
Number of sites, investigation completed | site							16						16
Number of sites investigation in progress | site							3						3
Number of sites remediation for soil and groundwater contamination | site							14						14
Environmental							$ 20,500,000	$ 36,000,000.0					$ 20,500,000
Number of other potentially responsible parties | site	120						70
Estimate of cost																			$ 726,000,000
Estimate low end				$ 165,000,000
Estimated development time				4 years
Investigate sites notice from EPA | site												6
Provision for new losses		$ 1,900,000							$ 1,000,000.0	$ 1,100,000		$ 1,100,000
Investigative sites | site												8
Accrual component amount							$ 1,900,000						1,900,000
Number of residences above applicable screening levels | residence						3
Number of sampling events below applicable screening levels | sampling_event						2
Loss contingency percentage of damages allocated to company			65.00%
Loss contingency percentage of damages allocated to counterparty			35.00%
Estimate of possible loss | €																€ 0.4
Estimated insurance recoveries							25,000,000						25,000,000
Insurance recoveries to date							22,000,000
Estimated recovery for non-GST Trust claimants							10,000,000						10,000,000
Threshold of recovery before shared in trust							3,000,000						3,000,000
Lower Passaic River Study Area, Focused Feasibility Study, April 11, 2014
Site Contingency [Line Items]
Environmental							2,700,000						2,700,000							$ 3,500,000
Onondaga Site EPA Remedial Investigation
Site Contingency [Line Items]
Environmental							0						0	$ 10,000,000.0
Coltec Industries Inc.
Site Contingency [Line Items]
Environmental							4,300,000						$ 4,300,000				$ 1,300,000
Provision for new losses									$ 3,500,000		$ 5,700,000
Payments for environmental loss contingencies							$ 4,500,000
Minimum
Site Contingency [Line Items]
Loss exposure in excess of accrual | €			€ 7.9
Site contingency, loss exposure in excepss of accrual best estimate | €			1.8
Estimate of possible loss | €			5.1
Loss accrual | €			0.4
Maximum
Site Contingency [Line Items]
Portion of site subject to remediation | mi							9						9
Loss exposure in excess of accrual | €			10.2
Site contingency, loss exposure in excepss of accrual best estimate | €			2.1
Estimate of possible loss | €			€ 6.6
Arizona
Site Contingency [Line Items]
Investigate sites notice from EPA										2								6			2
Mississippi
Site Contingency [Line Items]
Provision for new losses					$ 3,000,000.0			$ 4,700,000
Number of property owners | property															27
Environmental Remediation
Site Contingency [Line Items]
Loss in period													$ 800,000
Asbestos Issue
Site Contingency [Line Items]
Insurance coverage amount							$ 5,500,000						5,500,000
Insurance available for future claims							5,500,000						5,500,000
Estimated insurance recoveries, year one							5,500,000						5,500,000
Asbestos Issue | GST, LLC
Site Contingency [Line Items]
Amount recovered							$ 8,800,000						$ 8,800,000
Affiliated Entity | Crucible Steel Corporation
Site Contingency [Line Items]
Portion of site subject to remediation | mi								17