Commitments and Contingent Liabilities (Details) $ in Millions	3 Months Ended			12 Months Ended	36 Months Ended	74 Months Ended
	Mar. 31, 2020 USD ($) payment shares	Dec. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)	Feb. 03, 2017 USD ($)	Mar. 31, 2020 USD ($) shares
Other Commitments [Abstract]
ZAI PD account funding					$ 49.4
ZAI P D account, maximum number of contingent deferred payments | payment	10
ZAI P D account, deferred payments, each year for twenty years	$ 8.0
Period in which ZAI PD contingent deferred payments will be made	20 years
Minimum ZAI P D account assets for condition in relation to contingent obligation payments	$ 10.0					$ 10.0
ZAI PD Claims and Expenses paid by the Trust						32.0
ZAI PD Attorney's fees paid by the Trust					$ 15.0
ZAI PD Trust Balance	$ 20.0					$ 20.0
Frequency of PD trust payments	6 months
Estimated annual expenses related to PD Trust	$ 0.2
Number of shares issuable under warrant (in shares) | shares	77,372,257					77,372,257
Period within which contingent funding obligations are reasonably estimable	5 years
Period Covered by Reserve for Loss Contingency	5 years
Legacy Matters
Accrual for Environmental Loss Contingencies	$ 112.8	$ 115.3		$ 115.3		$ 112.8
Legacy Product Charge		24.0
Remaining Period in Which ZAI PD Contingent Deferred Payments May be Made	19 years
Total Maximum Financial Obligation for ZAI PD Account Contingent Deferred Payments	$ 80.0
Maximum Annual Obligation for ZAI PD Account Contingent Deferred Payments	8.0
Non-Vermiculite Related Matters
Legacy Matters
Accrual for Environmental Loss Contingencies	38.9	39.3		39.3		38.9
Vermiculite Related Matters
Legacy Matters
Accrual for Environmental Loss Contingencies	73.9	$ 76.0		76.0		73.9
Operable Unit 3 [Member]
Legacy Matters
Environmental Remediation Expense			$ 70.0
Spillway [Member]
Legacy Matters
Loss Contingency, Loss in Period				$ 68.0
Minimum | Operable Unit 3 [Member]
Legacy Matters
Loss Contingency, Estimate of Possible Loss	30.0					30.0
Minimum | Spillway [Member]
Legacy Matters
Loss Contingency, Estimate of Possible Loss	$ 50.0					50.0
Site Contingency, Time Frame of Disbursements	three years
Maximum | Operable Unit 3 [Member]
Legacy Matters
Loss Contingency, Estimate of Possible Loss	$ 170.0					170.0
Maximum | Spillway [Member]
Legacy Matters
Loss Contingency, Estimate of Possible Loss	$ 100.0					100.0
Site Contingency, Time Frame of Disbursements	P4Y
ZAI PD Trust [Member] | Minimum
Legacy Matters
Loss Contingency, Estimate of Possible Loss	$ 16.0					16.0
ZAI PD Trust [Member] | Maximum
Legacy Matters
Loss Contingency, Estimate of Possible Loss	$ 24.0					$ 24.0