Commitments and Contingent Liabilities (Details)	3 Months Ended		9 Months Ended	12 Months Ended	36 Months Ended	80 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2020 USD ($) payment shares	Dec. 31, 2019 USD ($)	Feb. 03, 2017 USD ($)	Sep. 30, 2020 USD ($) shares
Other Commitments [Abstract]
ZAI PD account funding					$ 49,400,000
ZAI P D account, maximum number of contingent deferred payments | payment			10
ZAI P D account, deferred payments, each year for twenty years			$ 8,000,000
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			$ 10,000,000			$ 10,000,000
ZAI PD Claims and Expenses paid by the Trust						36,000,000
ZAI PD Attorney's fees paid by the Trust					$ 15,000,000
ZAI PD Trust Balance			$ 19,000,000			$ 19,000,000
Frequency of PD trust payments			6 months
Estimated annual expenses related to PD Trust			$ 200,000
Number of shares issuable under warrant (in shares) | shares			77,372,257			77,372,257
Legacy Matters
Accrual for Environmental Loss Contingencies	$ 115,300,000		$ 110,700,000	$ 115,300,000		$ 110,700,000
Legacy Product Charge	24,000,000.0
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			$ 80,000,000.0
Maximum Annual Obligation for ZAI PD Account Contingent Deferred Payments			8,000,000.0
Non-Vermiculite Related Matters
Legacy Matters
Accrual for Environmental Loss Contingencies	39,300,000		38,300,000	39,300,000		38,300,000
Vermiculite Related Matters
Legacy Matters
Accrual for Environmental Loss Contingencies	$ 76,000,000.0		72,400,000	76,000,000.0		72,400,000
Operable Unit 3 [Member]
Legacy Matters
Environmental Remediation Expense		$ 70,000,000.0
Spillway [Member]
Legacy Matters
Loss Contingency, Estimate of Possible Loss			95,000,000.0			95,000,000.0
Loss Contingency, Loss in Period			27,000,000.0	$ 68,000,000.0
Minimum | Operable Unit 3 [Member]
Legacy Matters
Loss Contingency, Estimate of Possible Loss			30,000,000			30,000,000
Minimum | Spillway [Member]
Legacy Matters
Loss Contingency, Estimate of Possible Loss			$ 80,000,000			80,000,000
Site Contingency, Time Frame of Disbursements			three years
Maximum | Operable Unit 3 [Member]
Legacy Matters
Loss Contingency, Estimate of Possible Loss			$ 170,000,000			170,000,000
Maximum | Spillway [Member]
Legacy Matters
Loss Contingency, Estimate of Possible Loss			$ 120,000,000			120,000,000
Site Contingency, Time Frame of Disbursements			P4Y
ZAI PD Trust [Member] | Minimum
Legacy Matters
Loss Contingency, Estimate of Possible Loss			$ 16,000,000			16,000,000
ZAI PD Trust [Member] | Maximum
Legacy Matters
Loss Contingency, Estimate of Possible Loss			$ 24,000,000			$ 24,000,000