CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 6.5	$ (2.8)	$ 0.9	$ (2.6)	$ 3.7	$ (1.7)
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization					48.6	47.9
Amortization of debt issuance costs					1.0	0.9
Change in value of contingent consideration	(5.8)		0.3		(5.5)	1.3
Loss (gain) on sale/disposal of assets, net					(0.1)	1.0
Gains from eminent domain matter and property insurance claims					0.0	(6.0)
Deferred income taxes					2.6	2.5
Provision for doubtful accounts and customer disputes					1.0	1.3
Stock-based compensation					6.2	11.1
Other, net					(0.8)	(0.6)
Changes in assets and liabilities, excluding effects of acquisitions:
Accounts receivable					24.9	(13.1)
Inventories					1.7	(1.6)
Prepaid expenses and other current assets					(3.0)	(4.6)
Other assets and liabilities					2.7	(0.7)
Accounts payable and accrued liabilities					1.1	2.9
Net cash provided by operating activities					84.1	40.6
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property, plant and equipment					(14.2)	(18.1)
Payment for acquisition of business					(140.2)	0.0
Proceeds from sale of businesses and property, plant and equipment					0.3	0.7
Proceeds from eminent domain matter and property insurance claims					0.0	6.0
Net cash used in investing activities					(154.1)	(11.4)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolver borrowings					260.8	163.3
Repayments of revolver borrowings					(204.3)	(157.8)
Proceeds from stock option exercises					0.0	0.2
Payments of other long-term obligations					(9.9)	(11.6)
Payments for finance leases, promissory notes and other					(10.8)	(16.2)
Proceeds from finance lease and other					14.5		$ 0.0
Debt issuance costs					(2.2)	0.0
Shares redeemed for employee income tax obligations					(1.2)	(2.2)
Net cash provided by (used in) financing activities					46.9	(24.3)
EFFECT OF EXCHANGE RATES ON CASH AND CASH EQUIVALENTS					0.0	(0.1)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS					(23.1)	4.8
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD		$ 40.6		$ 20.0	40.6	20.0	20.0
CASH AND CASH EQUIVALENTS AT END OF PERIOD	17.5		24.8		17.5	24.8	$ 40.6
Supplemental Disclosure of Cash Flow Information:
Net cash paid for interest					22.6	22.6
Net cash paid for (refund from) income taxes					(0.1)	0.6
Supplemental Disclosure of Non-cash Investing and Financing Activities:
Capital expenditures funded by finance leases and promissory notes					13.7	13.0
Acquisitions funded by deferred consideration	$ 1.7		$ 0.0		1.7	0.0
Transfer of non-controlling interest					$ 3.3	$ 0.0