Cash Flow Statement- Supplemental Information - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Supplemental Cash Flow Information [Abstract]
Acquisition of net assets	$ 0.7
Deferred tax assets, net	21.1
Deferred tax liabilities, net	0.1
Deferred credits	20.3
Accounts receivable and unbilled, net	0.6
Other assets	$ 0.1