Revenue Recognition (Tables)

6 Months Ended

Jun. 30, 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
	June 30, 2021
	Products and Services		Freight		Total
	(Dollars in Millions)
East Group	$	596.5	$	38.8	$	635.3
West Group		628.8		38.0		666.8
Total Building Materials business		1,225.3		76.8		1,302.1
Magnesia Specialties		70.0		5.8		75.8
Total	$	1,295.3	$	82.6	$	1,377.9
	Three Months Ended
	June 30, 2020
	Products and Services		Freight		Total
	(Dollars in Millions)
East Group	$	499.7	$	34.8	$	534.5
West Group		640.9		41.6		682.5
Total Building Materials business		1,140.6		76.4		1,217.0
Magnesia Specialties		48.9		4.7		53.6
Total	$	1,189.5	$	81.1	$	1,270.6

	Six Months Ended
	June 30, 2021
	Products and Services		Freight		Total
	(Dollars in Millions)
East Group	$	969.1	$	61.1	$	1,030.2
West Group		1,112.9		70.5		1,183.4
Total Building Materials business		2,082.0		131.6		2,213.6
Magnesia Specialties		135.2		11.5		146.7
Total	$	2,217.2	$	143.1	$	2,360.3
	Six Months Ended
	June 30, 2020
	Products and Services		Freight		Total
	(Dollars in Millions)
East Group	$	857.6	$	58.9	$	916.5
West Group		1,114.1		79.0		1,193.1
Total Building Materials business		1,971.7		137.9		2,109.6
Magnesia Specialties		108.8		10.5		119.3
Total	$	2,080.5	$	148.4	$	2,228.9

Summary of Information About the Company's Contract Balances

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

(Dollars in Millions)	June 30, 2021		December 31, 2020
Costs in excess of billings	$	12.1	$	2.2
Billings in excess of costs	$	9.9	$	14.0