Commitments, Contingencies and Litigation Settlement (Details) - USD ($) $ in Millions	1 Months Ended				3 Months Ended	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Sep. 30, 2013	May 31, 2013	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Litigation settlement gain					$ 3.3	$ 3.3	$ 0.0	$ (2.2)
TMK IPSCO
Loss Contingencies [Line Items]
Damages awarded		$ 2.2	$ 5.2
Loss contingency accrual	$ 7.3				$ 7.3
Direct Damages | TMK IPSCO
Loss Contingencies [Line Items]
Direct damages sought				$ 10.0
Settled Litigation | TMK IPSCO
Loss Contingencies [Line Items]
Payments for legal settlements	$ 4.0