SEGMENT INFORMATION - Capital Expenditures (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Payments to acquire property, plant, and equipment	$ 13.6	$ 6.9	$ 46.0	$ 14.2
Operating segment | Ready-mixed concrete
Segment Reporting Information [Line Items]
Payments to acquire property, plant, and equipment	10.4	4.3	11.5	8.7
Operating segment | Ready-mixed concrete | Stockton Terminal Facility
Segment Reporting Information [Line Items]
Payments to acquire property, plant, and equipment	8.2		8.2
Operating segment | Aggregate Products
Segment Reporting Information [Line Items]
Payments to acquire property, plant, and equipment	2.9	2.5	34.0	5.3
Operating segment | Aggregate Products | Orca acquisition
Segment Reporting Information [Line Items]
Payments to acquire property, plant, and equipment			28.7
Other products and corporate
Segment Reporting Information [Line Items]
Payments to acquire property, plant, and equipment	$ 0.3	$ 0.1	$ 0.5	$ 0.2