Revenue Recognition (Tables)

3 Months Ended

Mar. 31, 2021

Revenue From Contract With Customer [Abstract]

Schedule of Company's Total Revenues by Category for each Reportable Segment

The following table presents the Company’s total revenues by category for each reportable segment.

	Three Months Ended
	March 31, 2021
	Products and Services		Freight		Total
	(Dollars in Millions)
East Group	$	372.5	$	22.4	$	394.9
West Group		484.1		32.5		516.6
Total Building Materials business		856.6		54.9		911.5
Magnesia Specialties		65.3		5.6		70.9
Total	$	921.9	$	60.5	$	982.4
	Three Months Ended
	March 31, 2020
	Products and Services		Freight		Total
	(Dollars in Millions)
East Group	$	357.9	$	24.0	$	381.9
West Group		473.2		37.4		510.6
Total Building Materials business		831.1		61.4		892.5
Magnesia Specialties		59.9		5.8		65.7
Total	$	891.0	$	67.2	$	958.2

Summary of Information About the Company's Contract Balances

The following table presents information about the Company’s contract balances:

(Dollars in Millions)	March 31, 2021		December 31, 2020
Costs in excess of billings	$	1.4	$	2.2
Billings in excess of costs	$	11.6	$	14.0