Income Tax Expense (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Income Tax Expense [Line Items]
Accumulated unremitted earnings of foreign subsidiaries				$ 3,500
Income taxes due if foreign entities' earnings were distributed				300
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				100		$ 100
Operating Loss Carryforwards, Valuation Allowance				600		400
Net operating loss carryforward - foreign				4,603		4,486
Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration				16,700
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration				2,300
Deferred Tax Assets, Operating Loss Carryforwards, State and Local				600
Deferred Tax Assets, Tax Credit Carryforwards, Research				2,100
State Research And Other Credit CarryForwards With Expiration Date				1,700
State Research And Other Credit Carry Forwards Without Expiration Date				400
Deferred Tax Assets, Valuation Allowance				7,144		4,440
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount				$ 2,700		$ 1,300
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				24.50%	35.00%	35.00%	35.00%
Effective Income Tax Reduction on Deferred tax Liabilities				$ 30,700
Effective Income Tax Benefit from Pension Contribution	$ 1,000
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 7,500			10,200		$ 2,900
Effective Income Tax Benefit from Change in Tax Accounting method		$ 1,000
Effective Income Tax Provisional Charge Transition Tax				3,700
Effective Income Taxes Foreign Withholding Taxes				2,400
Unrecognized Tax Benefits				100
Excess Foreign Tax Credits [Member]
Income Tax Expense [Line Items]
Tax Credit Carryforward, Amount				2,400
FINLAND
Income Tax Expense [Line Items]
Deferred Tax Assets, Net				200
Deferred Tax Assets, Operating Loss Carryforwards				2,200
Scenario, Forecast [Member]
Income Tax Expense [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%
Foreign Valuation Allowance [Member]
Income Tax Expense [Line Items]
Operating Loss Carryforwards, Valuation Allowance				3,800		3,700
State and Local Jurisdiction [Member]
Income Tax Expense [Line Items]
Operating Loss Carryforwards, Valuation Allowance				400		$ 400
Net operating loss carryforward - foreign				$ 19,000