Revenues and Gross Profit - Total Revenues and Gross Profit by Product Line (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Product Information [Line Items]
Total revenues	$ 958.2	$ 939.0
Gross profit (loss)	142.4	142.9
Interproduct Revenues
Product Information [Line Items]
Total revenues	(53.6)	(58.4)
Corporate
Product Information [Line Items]
Gross profit (loss)	(1.0)	(0.4)
Building Materials Business
Product Information [Line Items]
Total revenues	892.5	864.9
Building Materials Business | Operating Segments
Product Information [Line Items]
Total revenues	892.5	864.9
Gross profit (loss)	118.2	117.8
Building Materials Business | Operating Segments | Products and Services
Product Information [Line Items]
Total revenues	831.1	809.1
Gross profit (loss)	118.5	118.0
Magnesia Specialties | Operating Segments
Product Information [Line Items]
Total revenues	65.7	74.1
Gross profit (loss)	25.2	25.5
Magnesia Specialties | Operating Segments | Products and Services
Product Information [Line Items]
Total revenues	59.9	69.2
Gross profit (loss)	26.1	26.5
Aggregates | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	570.3	544.9
Gross profit (loss)	93.4	98.0
Cement | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	106.6	99.0
Gross profit (loss)	27.3	13.8
Ready Mixed Concrete | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	189.7	211.2
Gross profit (loss)	5.9	14.5
Asphalt and Paving | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	18.1	12.4
Gross profit (loss)	(8.1)	(8.3)
Freight
Product Information [Line Items]
Total revenues	67.2	60.7
Freight | Building Materials Business
Product Information [Line Items]
Total revenues	61.4	55.8
Freight | Building Materials Business | Operating Segments
Product Information [Line Items]
Total revenues	61.4	55.8
Gross profit (loss)	(0.3)	(0.2)
Freight | Magnesia Specialties | Operating Segments
Product Information [Line Items]
Total revenues	5.8	4.9
Gross profit (loss)	$ (0.9)	$ (1.0)