Income Taxes (Details) - USD ($) $ in Thousands  | 
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2018  | 
Sep. 30, 2017  | 
Sep. 30, 2018  | 
Sep. 30, 2017  | 
|
| Income Taxes | ||||
| Effective tax rate (as a percent) | 10.40% | 38.10% | 18.90% | 33.90% | 
| Reserve for uncertain tax positions | $ 1,258 | $ 763 | ||
| Voluntary pension funding | 7,000 | |||
| Increased pension funding deduction | $ 651 | |||
| X | ||||||||||
- Definition Amount of voluntary pension funding. No definition available. 
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| X | ||||||||||
- Definition Amount of income tax benefit due to increased pension funding deduction. No definition available. 
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| X | ||||||||||
- Definition Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
- References No definition available. 
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| X | ||||||||||
- Definition Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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