BUSINESS COMBINATION - PROFORMA (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pro-forma Combined
Operating revenue	$ 543.9	$ 505.4	$ 1,530.8	$ 1,454.9
Net income	$ 34.1	$ 26.6	$ 65.1	$ 65.3
Basic Earnings Per Share (in dollars per share)	$ 0.79	$ 0.62	$ 1.51	$ 1.52
Diluted Earnings Per Share (in dollars per share)	$ 0.79	$ 0.62	$ 1.50	$ 1.50
Weighted Average Number of Shares Outstanding:
Basic	42.9	42.8	43.0	43.1
Diluted	43.2	43.2	43.3	43.5

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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Amount after tax of pro forma income from continuing operations as if the business combination had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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