Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Income Taxes
Noncurrent income taxes payable	$ 26,000			$ 0
Statutory tax rate	35.00%	21.00%	24.50%
Unrecognized Tax Benefits	$ 18,997			20,132
Estimated decrease in liability for unrecognized tax benefits	8,901
Unrecognized tax benefits that, if recognized, would affect the effective tax rate	8,949			9,677
Accrued interest and penalties	$ 1,243			$ 1,123

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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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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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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