LONG-TERM DEBT: Narrative (Details) - USD ($) $ in Millions		3 Months Ended	6 Months Ended	9 Months Ended
	Jun. 20, 2017	Sep. 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Term loans
Debt Instrument [Line Items]
Aggregate amount of borrowing commitment		$ 600.0	$ 600.0
Term loans | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Long-term debt variable interest rate description			LIBOR
Long-term debt basis spread on variable interest rate (as a percent)		2.00%
Term loans | Alternative Base Rate
Debt Instrument [Line Items]
Long-term debt variable interest rate description		Alternative base rate
Revolving credit facility
Debt Instrument [Line Items]
Total long-term debt and capital leases	$ 230.0
Repayments on lines of credit			$ 225.0
Fees related to the restated credit agreement			4.0
Aggregate amount of borrowing commitment		$ 150.0	$ 150.0
Weighted average interest rate on long-term debt (as a percent)		3.30%	3.30%
Revolving credit facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Long-term debt variable interest rate description				LIBOR
Revolving credit facility | Alternative Base Rate
Debt Instrument [Line Items]
Long-term debt variable interest rate description		Alternative base rate