Income Taxes (Narratives)(Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
TaxBenefitFromRemeasurementofDeferredTaxesDuetoTaxReform	$ 33,400
transition tax on the deemed dividend on foreign earnings	1,600
other tax impacts related to tax reform	$ 400
U.S. federal statutory tax rate	35.00%	35.00%	35.00%
Operating Loss Carryforwards, Valuation Allowance	$ 1,200	$ 1,200
Accumulated net earning	428,419	315,573
Gross deferred tax assets	18,600	34,400
Gross deferred tax liabilities	86,800	107,500
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	430	$ 1,293	$ 814
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0
Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	5,700
Accumulated net earning	$ 7,900