Commitments and Contingencies - Additional Information (Detail) - USD ($)			1 Months Ended
	May 08, 2018	Jan. 05, 2018	Mar. 31, 2018	Sep. 30, 2018
Commitments And Contingencies [Line Items]
Letters of credit outstanding, amount				$ 7,800,000
Outstanding guarantees				0
Contingently liable for performance, current				$ 27,700,000
American Gypsum Company LLC [Member] | Homebuilder Settlement Agreement [Member]
Commitments And Contingencies [Line Items]
Litigation settlement amount	$ 6,000,000
American Gypsum Company LLC [Member] | Direct and Indirect Purchaser Class [Member] | Direct and Indirect Purchaser Settlement Agreements [Member]
Commitments And Contingencies [Line Items]
Litigation settlement amount		$ 39,100,000
Amount deposited to qualified settlement fund			$ 38,800,000