SIGNIFICANT ACCOUNTING POLICIES - ACCUMULATED OTHER COMPREHENSIVE INCOME LOSS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	$ 471.5
Net gain in prior service cost		$ 0.7
Amortization of prior service cost	(0.4)	(0.4)
Amortization of net loss	0.9	1.1
Other adjustments	0.2	(0.1)
Balance at the end of the period	466.1
Pension Benefits
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(41.4)	(41.7)
Amortization of prior service cost	(0.4)	(0.4)
Amortization of net loss	0.8	0.8
Balance at the end of the period	(41.0)	(41.3)
Post Retirement
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(4.4)	(4.7)
Net gain in prior service cost		0.7
Amortization of net loss	0.1	0.2
Balance at the end of the period	(4.3)	(3.8)
Non-Qualified Plans
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(0.4)	(0.2)
Amortization of net loss		0.1
Balance at the end of the period	(0.4)	(0.1)
Other
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	0.1	(0.3)
Other adjustments	0.2	(0.1)
Balance at the end of the period	0.3	(0.4)
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(46.1)	(46.9)
Net gain in prior service cost		0.7
Amortization of prior service cost	(0.4)	(0.4)
Amortization of net loss	0.9	1.1
Other adjustments	0.2	(0.1)
Balance at the end of the period	$ (45.4)	$ (45.6)