Revenue Recognition - Schedule of Company's Total Revenues by Category for each Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue Recognition [Line Items]
Total	$ 982.4	$ 958.2
Building Materials Business
Revenue Recognition [Line Items]
Total	911.5	892.5
Products and Services
Revenue Recognition [Line Items]
Total	921.9	891.0
Products and Services | Building Materials Business
Revenue Recognition [Line Items]
Total	856.6	831.1
Freight
Revenue Recognition [Line Items]
Total	60.5	67.2
Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	54.9	61.4
Operating Segments | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	394.9	381.9
Operating Segments | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	516.6	510.6
Operating Segments | Building Materials Business
Revenue Recognition [Line Items]
Total	911.5	892.5
Operating Segments | Magnesia Specialties
Revenue Recognition [Line Items]
Total	70.9	65.7
Operating Segments | Products and Services | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	372.5	357.9
Operating Segments | Products and Services | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	484.1	473.2
Operating Segments | Products and Services | Magnesia Specialties
Revenue Recognition [Line Items]
Total	65.3	59.9
Operating Segments | Freight | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	22.4	24.0
Operating Segments | Freight | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	32.5	37.4
Operating Segments | Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	54.9	61.4
Operating Segments | Freight | Magnesia Specialties
Revenue Recognition [Line Items]
Total	$ 5.6	$ 5.8