Revenues and Gross Profit - Total Revenues and Gross Profit by Product Line (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Product Information [Line Items]
Total revenues	$ 982.4	$ 958.2
Gross profit (loss)	174.7	142.4
Interproduct Revenues
Product Information [Line Items]
Total revenues	(73.1)	(53.6)
Corporate
Product Information [Line Items]
Gross profit (loss)	(0.8)	(1.0)
Building Materials Business
Product Information [Line Items]
Total revenues	911.5	892.5
Building Materials Business | Operating Segments
Product Information [Line Items]
Total revenues	911.5	892.5
Gross profit (loss)	148.0	118.2
Building Materials Business | Operating Segments | Products and Services
Product Information [Line Items]
Total revenues	856.6	831.1
Gross profit (loss)	148.3	118.5
Magnesia Specialties | Operating Segments
Product Information [Line Items]
Total revenues	70.9	65.7
Gross profit (loss)	27.5	25.2
Magnesia Specialties | Operating Segments | Products and Services
Product Information [Line Items]
Total revenues	65.3	59.9
Gross profit (loss)	28.4	26.1
Aggregates | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	572.6	570.3
Gross profit (loss)	121.8	93.4
Cement | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	109.6	106.6
Gross profit (loss)	15.3	27.3
Ready Mixed Concrete | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	235.3	189.7
Gross profit (loss)	19.4	5.9
Asphalt and Paving | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	12.2	18.1
Gross profit (loss)	(8.2)	(8.1)
Freight
Product Information [Line Items]
Total revenues	60.5	67.2
Freight | Building Materials Business
Product Information [Line Items]
Total revenues	54.9	61.4
Freight | Building Materials Business | Operating Segments
Product Information [Line Items]
Total revenues	54.9	61.4
Gross profit (loss)	(0.3)	(0.3)
Freight | Magnesia Specialties | Operating Segments
Product Information [Line Items]
Total revenues	5.6	5.8
Gross profit (loss)	$ (0.9)	$ (0.9)