Income Taxes (Narrative) (Details)	3 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) tax_year	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Income Tax Contingency [Line Items]
Income taxes	$ 2,000,000	$ 50,000,000		$ 0
Deemed Repatriation Tax				0
Increase associated with Tax on undistributed earnings deferred tax liability				9.0
Other reconciling items				0.2
Decrease to overall net deferred tax liability				0
Deemed repatriation tax payable	1,300,000
Change in enacted tax rate, amount	$ 500,000
Prepaid income taxes and taxes receivable applied against the deemed repatriation tax liability			$ 28,400,000	0	$ 0
Deemed repatriation tax payable		61,900,000	$ 32,200,000	61,900,000
Deferred tax revaluation			0.004
Benefit to tax rate, amount			$ 2,300,000
Reduction of valuation allowance			7,800,000
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount			9,100,000
Tax benefits from activities during the period			14,600,000	25,200,000	19,300,000
Unrecognized tax benefits		$ 13,600,000	11,000,000	13,600,000	16,700,000
Unrecognized tax benefits that would impact effective tax rate			$ 7,900,000
Resolution of tax audits that could reduce unrecognized tax benefits (term)			12 months
Decrease due to future utilization of U.S. state net operating losses			$ 11,000,000
Increase due to accelerated bonus depreciation			$ 14,300,000
Expiration dates, time period			20 years
Maximum operating loss carryforward expiring annually			$ 10.0
Permanent reinvestment on earnings			733,900,000
Provisional deferred taxes on foreign earnings			(200,000)	$ 12,200,000	$ 2,300,000
Cumulative undistributed earnings that are indefinitely reinvested			314,000,000
Resulting provisional incremental tax expense			$ 19,500,000
IRS
Income Tax Contingency [Line Items]
Number of tax years under audit | tax_year			4
Canada
Income Tax Contingency [Line Items]
Number of tax years under audit | tax_year			8