FINANCING ARRANGEMENTS (Narrative) (Details)						3 Months Ended			12 Months Ended
	Jul. 17, 2019 USD ($)	Jul. 02, 2019 USD ($)	Aug. 01, 2018 USD ($)	Jul. 19, 2018 USD ($)	Apr. 17, 2018	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Financing arrangements
Loss on early extinguishment of debt						$ 6,100,000		$ 2,500,000	$ 6,131,000	$ 2,488,000	$ 7,891,000
Effective interest rate (as a percent)									4.67%
Fair value of long-term obligations, including current portion							$ 1,600,000,000		$ 1,600,000,000	1,600,000,000
Borrowing from revolving credit facility									0	50,000,000	0
Settlement of borrowing									0	50,000,000	$ 0
Revolving credit facility, available borrowing capacity							235,400,000		229,200,000	235,400,000
Letters of credit outstanding, amount							130,100,000		146,900,000	130,100,000
Derivative liability							8,800,000		$ 20,800,000	8,800,000
Senior secured Term Loan Agreement
Financing arrangements
Term loan outstanding				$ 350,000,000.0
Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Repayments of debt				330,900,000
Accrued interest				7,900,000
Debt redemption fees				1,000,000.0
Term Loans with Interest Rate Swap Agreements
Financing arrangements
Debt outstanding							350,000,000.0			350,000,000.0
Unsecured debt
Financing arrangements
Redemption percentage of principal amount									100.00%
Debt instrument, redemption price, percentage of principal amount redeemed									35.00%
Unsecured debt | Unsecured senior notes, at 4.875%, due July 15, 2027 (2027 Notes)
Financing arrangements
Aggregate principal amount		$ 545,000,000.0
Redemption percentage of principal amount									104.875%
Interest rate (as a percent)									4.875%
Unsecured debt | Unsecured senior notes, at 5.125%, due July 15, 2029 (2029 Notes)
Financing arrangements
Aggregate principal amount		300,000,000.0
Redemption percentage of principal amount									105.125%
Interest rate (as a percent)									5.125%
Unsecured debt | Unsecured senior notes, at 5.125%, due June 1, 2021 (2021 Notes)
Financing arrangements
Interest rate (as a percent)									5.125%
Repurchased amount	$ 144,000,000.0	701,000,000.0
Repayments of debt		706,200,000
Accrued interest	$ 900,000	$ 3,100,000
Unsecured debt | Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Repurchased amount			$ 78,000,000.0	$ 322,000,000.0
Secured debt | Senior secured Term Loan Agreement
Financing arrangements
Effective interest rate (as a percent)									3.55%
Secured debt | Senior secured Term Loan Agreement | Base rate
Financing arrangements
Basis spread on variable rate (as a percent)					0.75%
Reduction of applicable interest rate margin					0.0025
Secured debt | Senior secured Term Loan Agreement | Eurodollar
Financing arrangements
Basis spread on variable rate (as a percent)					1.75%
Reduction of applicable interest rate margin					0.0025
LIne of credit
Financing arrangements
Credit facility, maximum borrowing capacity									$ 400,000,000.0
Period for measurement of average liquidity (in days)									30 days
LIne of credit | Minimum
Financing arrangements
Commitment fee (as a percent)									0.25%
LIne of credit | Minimum | Base rate
Financing arrangements
Basis spread on variable rate (as a percent)									0.25%
LIne of credit | Minimum | LIBOR
Financing arrangements
Basis spread on variable rate (as a percent)									1.25%
LIne of credit | Maximum
Financing arrangements
Commitment fee (as a percent)									0.30%
LIne of credit | Maximum | Base rate
Financing arrangements
Basis spread on variable rate (as a percent)									0.50%
LIne of credit | Maximum | LIBOR
Financing arrangements
Basis spread on variable rate (as a percent)									1.50%
LIne of credit | 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%
LIne of credit | 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%
Senior notes | Senior unsecured notes, at 5.25%, due August 1, 2020 (2020 Notes)
Financing arrangements
Redemption of 2020 notes			78,000,000.0
Interest rate swap
Financing arrangements
Basis spread on variable rate (as a percent)									2.92%
Notional amount							350,000,000.0			350,000,000.0
Revolving credit facility | LIne of credit
Financing arrangements
Borrowing from revolving credit facility			$ 50,000,000.0
Settlement of borrowing							50,000,000.0
Debt outstanding							$ 0		$ 0	$ 0
Revolving credit facility | LIne of credit | Parent and Domestic Subsidiaries
Financing arrangements
Credit facility, maximum borrowing capacity									300,000,000.0
Revolving credit facility | LIne of credit | Canadian Subsidiaries
Financing arrangements
Credit facility, maximum borrowing capacity									100,000,000.0
Letters of credit | LIne of credit | Parent and Domestic Subsidiaries
Financing arrangements
Credit facility, maximum borrowing capacity									250,000,000.0
Letters of credit | LIne of credit | Canadian Subsidiaries
Financing arrangements
Credit facility, maximum borrowing capacity									$ 75,000,000.0