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Stock-Based Compensation, Stock Award and Incentive Plan and Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Number of common stock available for issuance (in shares) |  |  | 880,000
Term of stock options granted under Plan | 10 years |  |
Vesting period, generally, for stock options granted under the plan | 3 years |  |
Share based compensation costs | $ 4,100 | $ 3,500 | $ 4,000
Tax benefit of share-based compensation | $ 1,100 | $ 1,400 | $ 1,600
Stock Options [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Forfeiture rate assumed | 8.71% | 7.38% | 7.34%
Weighted average grant date fair value for stock options granted (in dollars per share) | $ 30.28 | $ 14.34 | $ 22.68
Weighted average grant date fair value for stock options vested (in dollars per share) | $ 18.45 | $ 20.94 | $ 17.83
Total intrinsic value of stock options exercised | $ 11,700 | $ 4,900 | $ 2,400
Weighted Average Assumptions [Abstract] |  |  |
Expected life | 6 years 4 months 24 days | 6 years 5 months 23 days | 6 years 4 months 24 days
Interest rate | 2.04% | 1.72% | 1.52%
Volatility | 36.61% | 36.75% | 36.86%
Expected dividend yield | 0.26% | 0.54% | 0.33%
Stock Options [Roll Forward] |  |  |
Balance, beginning of year (in shares) | 1,198,725 |  |
Granted (in shares) | 187,533 |  |
Exercised (in shares) | (353,636) |  |
Canceled (in shares) | (35,783) |  |
Balance, end of year (in shares) | 996,839 | 1,198,725 |
Exercisable, end of year (in shares) | 596,446 |  |
Weighted Average Exercise Price Per Share [Abstract] |  |  |
Balance, beginning of year (in dollars per share) | $ 41.66 |  |
Granted (in dollars per share) | 77.99 |  |
Exercised (in dollars per share) | 41.56 |  |
Canceled (in dollars per share) | 50.47 |  |
Balance, end of year (in dollars per share) | 48.21 | $ 41.66 |
Exercisable, end of year (in dollars per share) | $ 41.01 |  |
Weighted Average Remaining Contractual Life [Abstract] |  |  |
Outstanding options, end of year | 6 years 3 months 25 days |  |
Exercisable options, end of year | 4 years 11 months 8 days |  |
Aggregate Intrinsic Value [Abstract] |  |  |
Outstanding options, end of year | $ 22,200 |  |
Exercisable options, end of year | $ 16,600 |  |
Additional Information [Abstract] |  |  |
Closing stock price on last business day of the period (in dollars per share) | $ 68.85 |  |
Weighted average intrinsic value of options exercised (in dollars per share) | $ 32.95 | $ 32.34 | $ 32.07
Unrecognized stock-based compensation expense | $ 4,500 |  |
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized | 3 years |  |
Nonvested Stock Options [Member] |  |  |
Stock Options [Roll Forward] |  |  |
Balance, beginning of year (in shares) | 431,412 |  |
Granted (in shares) | 187,533 |  |
Vested (in shares) | (183,679) |  |
Canceled (in shares) | (34,873) |  |
Balance, end of year (in shares) | 400,393 | 431,412 |
Weighted Average Exercise Price Per Share [Abstract] |  |  |
Balance, beginning of year (in dollars per share) | $ 45.61 |  |
Granted (in dollars per share) | 77.99 |  |
Vested (in dollars per share) | 48.78 |  |
Canceled (in dollars per share) | 50.08 |  |
Balance, end of year (in dollars per share) | $ 58.94 | $ 45.61 |
Restricted Stock [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Share based compensation costs | $ 5,900 | $ 5,800 | $ 8,800
Additional Information [Abstract] |  |  |
Unrecognized stock-based compensation expense | $ 5,100 |  |
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized | 3 years |  |

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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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