SIGNIFICANT ACCOUNTING POLICIES - ACCUMULATED OTHER COMPREHENSIVE INCOME LOSS (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period		$ 471.5			$ 471.5
Net gain in prior service cost	$ 0.1				0.1	$ 0.7
Amortization of prior service cost	(0.3)		$ (0.2)		(0.7)	(0.6)
Amortization of net loss	1.2		1.0		2.1	2.1
Other adjustments					0.2	(0.1)
Balance at the end of the period	475.9				475.9
Pensions
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(41.0)	(41.4)	(41.3)	$ (41.7)	(41.4)	(41.7)
Amortization of prior service cost	(0.3)	(0.4)	(0.3)	(0.4)
Amortization of net loss	0.8	0.8	0.8	0.8
Balance at the end of the period	(40.5)	(41.0)	(40.8)	(41.3)	(40.5)	(40.8)
Post Retirement
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(4.3)	(4.4)	(3.8)	(4.7)	(4.4)	(4.7)
Net gain in prior service cost				0.7
Amortization of net loss	0.3	0.1	0.2	0.2
Balance at the end of the period	(4.0)	(4.3)	(3.6)	(3.8)	(4.0)	(3.6)
Non-Qualified Plans
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(0.4)	(0.4)	(0.1)	(0.2)	(0.4)	(0.2)
Amortization of prior service cost			0.1
Amortization of net loss	0.1			0.1
Balance at the end of the period	(0.3)	(0.4)		(0.1)	(0.3)
Other
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	0.3	0.1	(0.4)	(0.3)	0.1	(0.3)
Net gain in prior service cost	0.1
Other adjustments		0.2		(0.1)
Balance at the end of the period	0.4	0.3	(0.4)	(0.4)	0.4	(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	(45.4)	(46.1)	(45.6)	(46.9)	(46.1)	(46.9)
Net gain in prior service cost	0.1			0.7
Amortization of prior service cost	(0.3)	(0.4)	(0.2)	(0.4)
Amortization of net loss	1.2	0.9	1.0	1.1
Other adjustments		0.2		(0.1)
Balance at the end of the period	$ (44.4)	$ (45.4)	$ (44.8)	$ (45.6)	$ (44.4)	$ (44.8)