Business Segments - Financial Data for Continuing Operations for Company's Reportable Business Segments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Total revenues	$ 982.4	$ 958.2
Earnings (Loss) from operations	99.3	57.8
Products and Services
Segment Reporting Information [Line Items]
Total revenues	921.9	891.0
Building Materials Business
Segment Reporting Information [Line Items]
Total revenues	911.5	892.5
Earnings (Loss) from operations	93.6	57.5
Building Materials Business | Products and Services
Segment Reporting Information [Line Items]
Total revenues	856.6	831.1
Operating Segments | Building Materials Business East Group
Segment Reporting Information [Line Items]
Total revenues	394.9	381.9
Earnings (Loss) from operations	61.7	34.8
Operating Segments | Building Materials Business East Group | Products and Services
Segment Reporting Information [Line Items]
Total revenues	372.5	357.9
Operating Segments | Building Materials Business West Group
Segment Reporting Information [Line Items]
Total revenues	516.6	510.6
Earnings (Loss) from operations	31.9	22.7
Operating Segments | Building Materials Business West Group | Products and Services
Segment Reporting Information [Line Items]
Total revenues	484.1	473.2
Operating Segments | Magnesia Specialties
Segment Reporting Information [Line Items]
Total revenues	70.9	65.7
Earnings (Loss) from operations	23.5	21.7
Operating Segments | Magnesia Specialties | Products and Services
Segment Reporting Information [Line Items]
Total revenues	65.3	59.9
Operating Segments | Building Materials Business
Segment Reporting Information [Line Items]
Total revenues	911.5	892.5
Corporate
Segment Reporting Information [Line Items]
Earnings (Loss) from operations	$ (17.8)	$ (21.4)