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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue Recognition [Line Items]
Total	$ 1,270.6	$ 1,279.5	$ 2,228.9	$ 2,218.4
Building Materials Business
Revenue Recognition [Line Items]
Total	1,217.0	1,203.2	2,109.6	2,068.1
Products and Services
Revenue Recognition [Line Items]
Total	1,189.5	1,196.1	2,080.5	2,074.4
Products and Services | Building Materials Business
Revenue Recognition [Line Items]
Total	1,140.6	1,125.7	1,971.7	1,934.9
Freight
Revenue Recognition [Line Items]
Total	81.1	83.4	148.4	144.0
Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	76.4	77.5	137.9	133.2
Operating Segments | Building Materials Business Mid-America Group
Revenue Recognition [Line Items]
Total	392.3	414.5	653.1	662.6
Operating Segments | Building Materials Business Southeast Group
Revenue Recognition [Line Items]
Total	142.2	137.0	263.4	256.3
Operating Segments | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	682.5	651.7	1,193.1	1,149.2
Operating Segments | Building Materials Business
Revenue Recognition [Line Items]
Total	1,217.0	1,203.2	2,109.6	2,068.1
Operating Segments | Magnesia Specialties
Revenue Recognition [Line Items]
Total	53.6	76.3	119.3	150.3
Operating Segments | Products and Services | Building Materials Business Mid-America Group
Revenue Recognition [Line Items]
Total	362.9	381.9	603.9	611.5
Operating Segments | Products and Services | Building Materials Business Southeast Group
Revenue Recognition [Line Items]
Total	136.8	132.0	253.7	247.4
Operating Segments | Products and Services | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	640.9	611.8	1,114.1	1,076.0
Operating Segments | Products and Services | Magnesia Specialties
Revenue Recognition [Line Items]
Total	48.9	70.4	108.8	139.5
Operating Segments | Freight | Building Materials Business Mid-America Group
Revenue Recognition [Line Items]
Total	29.4	32.6	49.2	51.1
Operating Segments | Freight | Building Materials Business Southeast Group
Revenue Recognition [Line Items]
Total	5.4	5.0	9.7	8.9
Operating Segments | Freight | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	41.6	39.9	79.0	73.2
Operating Segments | Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	76.4	77.5	137.9	133.2
Operating Segments | Freight | Magnesia Specialties
Revenue Recognition [Line Items]
Total	$ 4.7	$ 5.9	$ 10.5	$ 10.8