FINANCING ARRANGEMENTS (Narrative) (Details)				3 Months Ended	12 Months Ended
	Aug. 02, 2018	Aug. 01, 2018 USD ($)	Jul. 19, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2018 USD ($)	Apr. 17, 2018	Sep. 30, 2017	Mar. 14, 2016 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2012 USD ($)	Jul. 30, 2012 USD ($)
Financing arrangements
Borrowing from revolving credit facility					$ 50,000,000	$ 0	$ 0
Settlement of borrowing					50,000,000	0	$ 0
Revolving credit facility, available borrowing capacity				$ 235,400,000	235,400,000	217,800,000
Letters of credit outstanding, amount				130,100,000	130,100,000	134,100,000
Effective interest rate (as a percent)	4.67%
Derivative liability				8,800,000	$ 8,800,000
Eurodollar
Financing arrangements
Basis spread on variable rate (as a percent)	1.75%
Parent and Domestic Subsidiaries
Financing arrangements
Credit available subject to percentage of accounts receivable (as a percent)					85.00%
Credit available subject to percentage of cash deposited (as a percent)					100.00%
Canadian Subsidiaries
Financing arrangements
Credit available subject to percentage of accounts receivable (as a percent)					85.00%
Credit available subject to percentage of cash deposited (as a percent)					100.00%
Term Loan Agreement
Financing arrangements
Increase in principal amount of initial term loans			$ 350,000,000.0
Debt outstanding				742,200,000	$ 742,200,000
Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Purchase price			330,900,000
Accrued interest			7,900,000
Debt redemption fees			1,000,000
Term Loans with Interest Rate Swap Agreements
Financing arrangements
Debt outstanding								$ 350,000,000
Secured Debt | First Amendment | Eurodollar
Financing arrangements
Reduction of applicable interest rate margin									0.0025
Interest rate (as a percent)									1.75%
Secured Debt | First Amendment | Base rate loans
Financing arrangements
Reduction of applicable interest rate margin									0.0025
Interest rate (as a percent)									0.75%
Secured Debt | Term Loan Agreement
Financing arrangements
Fair value of notes				$ 707,000,000	$ 707,000,000	400,500,000
Effective interest rate (as a percent)										4.27%
Senior Notes | Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Interest rate (as a percent)				5.25%	5.25%									5.25%
Redemption of 2020 Notes		$ 78,000,000	$ 322,000,000
Fair value of notes						404,600,000
Face amount														$ 800,000,000
Repurchased amount				$ 400,000,000	$ 400,000,000	400,000,000.0
Senior Notes | Senior unsecured notes, at 5.125%, due June 1, 2021 (2021 Notes)
Financing arrangements
Interest rate (as a percent)				5.125%	5.125%								5.125%
Fair value of notes				$ 845,000,000	$ 845,000,000	855,700,000
Face amount											$ 250,000,000.0		$ 600,000,000.0
Repurchased amount												$ 5,000,000.0
Revolving credit facility
Financing arrangements
Revolving credit facility, maximum borrowing capacity				400,000,000.0	$ 400,000,000.0
Period for measurement of average liquidity (in days)					30 days
Revolving credit facility | Minimum
Financing arrangements
Commitment fee (as a percent)					0.25%
Revolving credit facility | Minimum | LIBOR loans
Financing arrangements
Basis spread on variable rate (as a percent)					1.25%
Revolving credit facility | Minimum | Base rate loans
Financing arrangements
Basis spread on variable rate (as a percent)					0.25%
Revolving credit facility | Maximum
Financing arrangements
Commitment fee (as a percent)					0.30%
Revolving credit facility | Maximum | LIBOR loans
Financing arrangements
Basis spread on variable rate (as a percent)					1.50%
Revolving credit facility | Maximum | Base rate loans
Financing arrangements
Basis spread on variable rate (as a percent)					0.50%
Revolving credit facility | Parent and Domestic Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity				300,000,000	$ 300,000,000
Revolving credit facility | Canadian Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity				100,000,000	100,000,000
Letters of credit | Parent and Domestic Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity				250,000,000	250,000,000
Letters of credit | Canadian Subsidiaries
Financing arrangements
Revolving credit facility, maximum borrowing capacity				75,000,000	75,000,000
Interest rate swap
Financing arrangements
Basis spread on variable rate (as a percent)	2.92%
Notional amount of interest rate swap agreements								$ 350,000,000.0
Revolving credit facility | Revolving credit facility
Financing arrangements
Borrowing from revolving credit facility		$ 50,000,000
Settlement of borrowing				50,000,000
Debt outstanding				$ 0	$ 0	$ 0