Carrying amount as of the balance sheet date of the unpaid sum of the known and estimated amounts payable to satisfy all domestic and foreign income tax obligations due beyond one year or the operating cycle, whichever is longer. Alternate captions include income taxes payable, noncurrent.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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The amount of the unrecognized tax benefit of a position taken for which it is reasonably possible that the total amount thereof will significantly increase or decrease within twelve months of the balance sheet date.

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Amount of unrecognized tax benefits.

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Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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Estimated carrying amount as of the balance sheet date of the unpaid sum of the current and noncurrent portions of one-time repatriation tax on deferred foreign income ("Transition Tax") obligations due beyond one year or the operating cycle, whichever is longer. The Transition Tax was a result of the enactment of the December 22, 2017 tax reform bill.

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Income Taxes [Line Items]

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Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended
Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Income Taxes [Line Items]
Net discrete impacts of the enactment of the Tax Act	$ 0	$ 14,778	$ 14,778
Total Accrued Transition Tax Liability	26,000		26,000
Current Accrued Transition Tax Liability	2,080		2,080
Noncurrent Accrued Transition Tax Liability	23,920		23,920
Noncurrent income taxes payable	23,920		23,920			$ 0
Statutory tax rate		35.00%		21.00%	24.50%
Unrecognized Tax Benefits	19,574		19,574			20,132
Estimated decrease in liability for unrecognized tax benefits	8,901		8,901
Unrecognized tax benefits that, if recognized, would affect the effective tax rate	9,176		9,176			9,677
Accrued interest and penalties	$ 1,372		$ 1,372			$ 1,123
Scenario, Forecast [Member]
Income Taxes [Line Items]
Statutory tax rate			21.00%