SEGMENT INFORMATION - Reconciliation of Total Reportable Segment Adjusted EBITDA to Income (Loss) From Continuing Operations (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) reporting_segment	Jun. 30, 2019 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | reporting_segment			2
Revenue by Segment:
Revenue	$ 322.7	$ 367.5	$ 657.1	$ 700.6
Reconciliation of Total Reportable Segment Adjusted EBITDA to Net Income:
Total reportable segment Adjusted EBITDA	59.7	50.3	102.7	95.2
Operating income	21.6	6.0	24.7	13.9
Depreciation, depletion and amortization for reportable segments	(25.2)	(25.1)	(48.6)	(47.9)
Interest expense, net	(11.4)	(11.6)	(22.8)	(23.2)
Change in value of contingent consideration for reportable segments	5.8	(0.3)	5.5	(1.3)
Realignment initiative costs	(0.8)	0.0	(0.8)	0.0
Eminent domain matter	0.0	5.3	0.0	5.3
Corporate, other products and eliminations other income (loss), net	0.6	7.2	1.2	7.6
Income (loss) before income taxes	10.8	1.6	3.1	(1.7)
Income tax benefit (expense)	(4.3)	(0.7)	0.6	0.0
Net income (loss)	6.5	0.9	3.7	(1.7)
Capital Expenditures:
Total capital expenditures			14.2	18.1
Ready-mixed concrete
Reconciliation of Total Reportable Segment Adjusted EBITDA to Net Income:
Total reportable segment Adjusted EBITDA	38.1	38.1	69.8	72.6
Aggregate products
Revenue by Segment:
Revenue	38.2	36.2	69.3	67.9
Reconciliation of Total Reportable Segment Adjusted EBITDA to Net Income:
Total reportable segment Adjusted EBITDA	21.6	12.2	32.9	22.6
Operating segment
Revenue by Segment:
Revenue	326.9	363.5	662.7	696.8
Reconciliation of Total Reportable Segment Adjusted EBITDA to Net Income:
Depreciation, depletion and amortization for reportable segments	(23.7)	(23.4)	(45.5)	(44.1)
Purchase accounting adjustments for inventory	(2.6)	0.0	(4.2)	0.0
Capital Expenditures:
Total capital expenditures	6.9	10.9	14.2	18.1
Operating segment | Ready-mixed concrete
Revenue by Segment:
Revenue	272.4	314.0	564.6	604.4
Capital Expenditures:
Total capital expenditures	4.3	5.8	8.7	11.6
Operating segment | Aggregate products
Revenue by Segment:
Revenue	54.5	49.5	98.1	92.4
Intersegment sales | Aggregate products
Revenue by Segment:
Revenue	16.3	13.3	28.8	24.5
Other products and eliminations
Revenue by Segment:
Revenue	(4.2)	4.0	(5.6)	3.8
Reconciliation of Total Reportable Segment Adjusted EBITDA to Net Income:
Operating income	0.3	1.6	0.4	1.5
Corporate, other products and eliminations other income (loss), net	(0.2)	0.0	(0.3)	0.4
Capital Expenditures:
Total capital expenditures	0.1	0.7	0.2	0.9
Corporate overhead
Reconciliation of Total Reportable Segment Adjusted EBITDA to Net Income:
Corporate overhead	(16.3)	(22.3)	(31.9)	(36.9)
Hurricane related losses
Reconciliation of Total Reportable Segment Adjusted EBITDA to Net Income:
Unusual or infrequent item	0.0	(2.1)	0.0	(2.1)
Mixer truck fire
Reconciliation of Total Reportable Segment Adjusted EBITDA to Net Income:
Unusual or infrequent item	$ 0.0	$ (0.1)	$ 0.0	$ (0.7)