Stock-Based Compensation Assumptions Used (Details) - Stock Options |
12 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
| Volatility | [1] | 20.90% | 24.30% | 24.30% | ||||
| Dividend yield | [2] | 0.50% | 0.60% | 0.60% | ||||
| Minimum [Member] | ||||||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
| Risk-free interest rate | 1.90% | 1.21% | 1.60% | |||||
| Expected years until exercise | 5 years 6 months | 5 years 6 months | 5 years 6 months | |||||
| Maximum [Member] | ||||||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||
| Risk-free interest rate | 2.26% | 1.77% | 2.20% | |||||
| Expected years until exercise | 8 years | 8 years | 8 years | |||||
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