SIGNIFICANT ACCOUNTING POLICIES - COMPREHENSIVE INCOME (LOSS) AND SUBSEQUENT EVENT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	$ 450.6	$ 363.8	$ 338.2
Net gain (loss) in prior service cost	0.7	5.1	(31.4)
Amortization of prior service cost	(1.3)	(1.3)	(1.3)
Amortization of net loss (gain)	1.2	1.8	2.5
Foreign currency translation and other adjustments	0.1	0.7	0.4
Other	0.1	0.1
Balance at the end of the period	471.5	450.6	363.8
Comprehensive Income (Loss):
Tax benefit (expense) on other comprehensive income (loss)	0.7	(5.0)	19.4
Pension Benefits
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(41.7)	(45.0)
Net gain (loss) in prior service cost		3.7
Amortization of prior service cost	(1.4)	(1.3)
Amortization of net loss (gain)	1.7	0.9
Balance at the end of the period	(41.4)	(41.7)	(45.0)
Post Retirement
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(4.7)	(7.2)
Net gain (loss) in prior service cost	0.7	1.4
Amortization of prior service cost		0.1
Amortization of net loss (gain)	(0.4)	1.0
Balance at the end of the period	(4.4)	(4.7)	(7.2)
Non-Qualified Plans
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(0.2)	(0.5)
Net gain (loss) in prior service cost	(0.1)	0.5
Amortization of prior service cost	(0.1)	(0.1)
Amortization of net loss (gain)		(0.1)
Balance at the end of the period	(0.4)	(0.2)	(0.5)
Foreign Currency Transaction
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	1.0	0.3
Foreign currency translation and other adjustments	0.1	0.7
Balance at the end of the period	1.1	1.0	0.3
Interest Hedge
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(0.6)	(0.7)
Other	0.1	0.1
Balance at the end of the period	(0.5)	(0.6)	(0.7)
Other
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(0.7)	(0.2)
Net gain (loss) in prior service cost	0.1	(0.5)
Amortization of prior service cost	0.2
Amortization of net loss (gain)	(0.1)
Balance at the end of the period	(0.5)	(0.7)	(0.2)
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(46.9)	(53.3)	(23.5)
Net gain (loss) in prior service cost	0.7	5.1
Amortization of prior service cost	(1.3)	(1.3)
Amortization of net loss (gain)	1.2	1.8
Foreign currency translation and other adjustments	0.1	0.7
Other	0.1	0.1
Balance at the end of the period	$ (46.1)	$ (46.9)	$ (53.3)