Revenue Recognition - Schedule of Company's Total Revenues by Category for each Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue Recognition [Line Items]
Total	$ 958.2	$ 939.0
Building Materials Business
Revenue Recognition [Line Items]
Total	892.5	864.9
Products and Services
Revenue Recognition [Line Items]
Total	891.0	878.3
Products and Services | Building Materials Business
Revenue Recognition [Line Items]
Total	831.1	809.1
Freight
Revenue Recognition [Line Items]
Total	67.2	60.7
Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	61.4	55.8
Operating Segments | Building Materials Business Mid-America Group
Revenue Recognition [Line Items]
Total	260.8	248.1
Operating Segments | Building Materials Business Southeast Group
Revenue Recognition [Line Items]
Total	121.1	119.2
Operating Segments | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	510.6	497.6
Operating Segments | Building Materials Business
Revenue Recognition [Line Items]
Total	892.5	864.9
Operating Segments | Magnesia Specialties
Revenue Recognition [Line Items]
Total	65.7	74.1
Operating Segments | Products and Services | Building Materials Business Mid-America Group
Revenue Recognition [Line Items]
Total	241.0	229.6
Operating Segments | Products and Services | Building Materials Business Southeast Group
Revenue Recognition [Line Items]
Total	116.9	115.3
Operating Segments | Products and Services | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	473.2	464.2
Operating Segments | Products and Services | Magnesia Specialties
Revenue Recognition [Line Items]
Total	59.9	69.2
Operating Segments | Freight | Building Materials Business Mid-America Group
Revenue Recognition [Line Items]
Total	19.8	18.5
Operating Segments | Freight | Building Materials Business Southeast Group
Revenue Recognition [Line Items]
Total	4.2	3.9
Operating Segments | Freight | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	37.4	33.4
Operating Segments | Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	61.4	55.8
Operating Segments | Freight | Magnesia Specialties
Revenue Recognition [Line Items]
Total	$ 5.8	$ 4.9