Revenue Recognition - Schedule of Company's Total Revenues by Category for each Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue Recognition [Line Items]
Total	$ 1,377.9	$ 1,270.6	$ 2,360.3	$ 2,228.9
Building Materials Business
Revenue Recognition [Line Items]
Total	1,302.1	1,217.0	2,213.6	2,109.6
Products and Services
Revenue Recognition [Line Items]
Total	1,295.3	1,189.5	2,217.2	2,080.5
Products and Services | Building Materials Business
Revenue Recognition [Line Items]
Total	1,225.3	1,140.6	2,082.0	1,971.7
Freight
Revenue Recognition [Line Items]
Total	82.6	81.1	143.1	148.4
Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	76.8	76.4	131.6	137.9
Operating Segments | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	635.3	534.5	1,030.2	916.5
Operating Segments | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	666.8	682.5	1,183.4	1,193.1
Operating Segments | Building Materials Business
Revenue Recognition [Line Items]
Total	1,302.1	1,217.0	2,213.6	2,109.6
Operating Segments | Magnesia Specialties
Revenue Recognition [Line Items]
Total	75.8	53.6	146.7	119.3
Operating Segments | Products and Services | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	596.5	499.7	969.1	857.6
Operating Segments | Products and Services | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	628.8	640.9	1,112.9	1,114.1
Operating Segments | Products and Services | Magnesia Specialties
Revenue Recognition [Line Items]
Total	70.0	48.9	135.2	108.8
Operating Segments | Freight | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	38.8	34.8	61.1	58.9
Operating Segments | Freight | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	38.0	41.6	70.5	79.0
Operating Segments | Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	76.8	76.4	131.6	137.9
Operating Segments | Freight | Magnesia Specialties
Revenue Recognition [Line Items]
Total	$ 5.8	$ 4.7	$ 11.5	$ 10.5