Share Repurchase Plan (Tables)

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Schedule of treasury stock by class

The following tables summarize share repurchase activity during the year ended December 31, 2017 and 2016 and the remaining authorized repurchase amount under the program as at December 31, 2017.

	Twelve Months Ended
(millions, except for share and per share data)	December 31, 2017		December 31, 2016
Total number of shares repurchased	—		305,183
Average price paid per share	$	—	$	24.43
Total value of shares repurchased	$	—	$	7.5

(millions)	December 31, 2017
Total authorized repurchase amount	$	30.0
Total value of shares repurchased	7.5
Total remaining authorized repurchase amount	$	22.5