Stock-Based Compensation (Details) $ / shares in Units, $ in Thousands | 12 Months Ended |
Dec. 31, 2016USD ($)$ / sharesshares | Dec. 31, 2015USD ($)$ / sharesshares | Dec. 31, 2014USD ($)shares |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | |
Annual percentage of outstanding shares available for grant, maximum | 5.00% | | |
Cumulative percentage of outstanding shares available for grant in a year, maximum | 10.00% | | |
Salaries, Wages and Officers' Compensation [Abstract] | | | |
Compensation expense, stock-based compensation | $ | $ 2,811 | $ 2,327 | $ 1,860 |
Income tax benefit | $ | $ 823 | $ 694 | $ 549 |
Employee Stock Purchase Plan [Abstract] | | | |
Employee stock purchase plan, service period | 1 year | | |
Employee stock purchase plan, percentage of market price, purchase date | 85.00% | | |
Employee stock purchase, discount from market price, purchase date | 15.00% | | |
Number of employees participating | 1,952 | 1,750 | 1,684 |
Shares purchased during the year | shares | 148,631 | 125,779 | 115,029 |
Cumulative shares purchased since 1982 | shares | 9,025,665 | 8,877,034 | 8,751,255 |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] | | | |
Volatility rate | 10.60% | 10.90% | 11.20% |
Risk-free interest rate | 1.80% | 2.10% | 2.60% |
Expected dividend yield | 0.70% | 0.70% | 1.10% |
Expected life of awards (years) | 9 years 6 months | 9 years 3 months 18 days | 9 years 4 months 24 days |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] | | | |
Outstanding, beginning balance | shares | 816,744 | | |
Granted | shares | 148,000 | | |
Exercised | shares | (137,696) | | |
Forfeited | shares | 27,400 | | |
Outstanding, ending balance | shares | 799,648 | 816,744 | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] | | | |
Exercisable, ending balance | shares | 375,448 | | |
Outstanding, weighted average exercise price, ending balance | $ 24.97 | $ 21.58 | |
Granted, weighted average exercise price | 32.70 | | |
Exercised, weighted average exercise price | 12.37 | | |
Forfeited, weighted average exercise price | 28.80 | | |
Exercisable, weighted average exercise price | $ 20.84 | | |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options | $ | $ 1,886 | | |
Exercisable, weighted average remaining contractual life (years) | 5 years 3 months 18 days | | |
Outstanding, aggregate intrinsic value | $ | $ 7,141 | | |
Exercisable, aggregate intrinisic value | $ | 4,903 | | |
Excess tax benefits | $ | 1,113 | $ 352 | $ 354 |
Employee stock option [Member] | | | |
Salaries, Wages and Officers' Compensation [Abstract] | | | |
Compensation expense, stock-based compensation | $ | $ 727 | 569 | 463 |
Employee stock option [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] | | | |
Outstanding, weighted average remaining contractual life (years) | 6 years 9 months 18 days | | |
Number outstanding | shares | 799,648 | | |
Outstanding options, weighted average exercise price | $ 24.97 | | |
Number exercisable | shares | 375,448 | | |
Exercisable options, weighted average exercise price | $ 20.84 | | |
Employee stock option [Member] | $16.00 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] | | | |
Lower range limit | 16 | | |
Upper range limit | $ 16 | | |
Number outstanding | shares | 88,853 | | |
Weighted average remaining contractual life (years) | 2 years 9 months 18 days | | |
Outstanding options, weighted average exercise price | $ 16 | | |
Number exercisable | shares | 88,853 | | |
Exercisable options, weighted average exercise price | $ 16 | | |
Employee stock option [Member] | Exercise Price Range, Range 2 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] | | | |
Lower range limit | 16.60 | | |
Upper range limit | $ 16.60 | | |
Number outstanding | shares | 95,095 | | |
Weighted average remaining contractual life (years) | 3 years 9 months 18 days | | |
Outstanding options, weighted average exercise price | $ 16.60 | | |
Number exercisable | shares | 95,095 | | |
Exercisable options, weighted average exercise price | $ 16.60 | | |
Employee stock option [Member] | Exercise Price Range, Range 3 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] | | | |
Lower range limit | 23.20 | | |
Upper range limit | $ 23.20 | | |
Number outstanding | shares | 181,650 | | |
Weighted average remaining contractual life (years) | 6 years 6 months | | |
Outstanding options, weighted average exercise price | $ 23.20 | | |
Number exercisable | shares | 102,250 | | |
Exercisable options, weighted average exercise price | $ 23.20 | | |
Employee stock option [Member] | Exercise Price Range, Range 4 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] | | | |
Lower range limit | 26.40 | | |
Upper range limit | $ 26.40 | | |
Number outstanding | shares | 173,050 | | |
Weighted average remaining contractual life (years) | 7 years 6 months | | |
Outstanding options, weighted average exercise price | $ 26.40 | | |
Number exercisable | shares | 62,950 | | |
Exercisable options, weighted average exercise price | $ 26.40 | | |
Employee stock option [Member] | Exercise Price Range, Range 5 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] | | | |
Lower range limit | 30.10 | | |
Upper range limit | $ 30.10 | | |
Number outstanding | shares | 133,500 | | |
Weighted average remaining contractual life (years) | 8 years 6 months | | |
Outstanding options, weighted average exercise price | $ 30.10 | | |
Number exercisable | shares | 26,300 | | |
Exercisable options, weighted average exercise price | $ 30.10 | | |
Employee stock option [Member] | Exercise Price Range, Range 6 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] | | | |
Lower range limit | 32.70 | | |
Upper range limit | $ 32.70 | | |
Number outstanding | shares | 127,500 | | |
Weighted average remaining contractual life (years) | 9 years 6 months | | |
Outstanding options, weighted average exercise price | $ 32.70 | | |
Number exercisable | shares | 0 | | |
Exercisable options, weighted average exercise price | $ 32.70 | | |
Stock Appreciation Rights (SARs) [Member] | | | |
Salaries, Wages and Officers' Compensation [Abstract] | | | |
Compensation expense, stock-based compensation | $ | $ 591 | $ 489 | 384 |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] | | | |
Vesting period | 5 years | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] | | | |
Unvested, beginning balance | shares | 330,707 | | |
Granted | shares | 150,100 | | |
Forfeited | shares | 0 | | |
Vested | shares | (108,976) | | |
Unvested, ending balance | shares | 371,831 | 330,707 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] | | | |
Unvested, weighted average award date value, beginning balance | $ 4.65 | | |
Granted, weighted average award date value | 6.38 | | |
Forfeited, weighted average award date value | 0 | | |
Vested, weighted average award date value | 4.11 | | |
Unvested, weighted average award date value, ending balance | $ 5.50 | $ 4.65 | |
Weighted average remaining contractual life (years) | 2 years 9 months 18 days | | |
Unrecognized compensation cost | $ | $ 1,515 | | |
Aggregate intrinsic value, unvested | $ | $ 12,605 | | |
Employee SSARs [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] | | | |
Unvested, ending balance | shares | 368,832 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] | | | |
Unvested, weighted average award date value, ending balance | $ 5.53 | | |
Weighted average remaining contractual life (years) | 2 years 10 months 24 days | | |
Unrecognized compensation cost | $ | $ 1,513 | | |
Aggregate intrinsic value, unvested | $ | 12,503 | | |
Equity Option [Member] | | | |
Salaries, Wages and Officers' Compensation [Abstract] | | | |
Compensation expense, stock-based compensation | $ | $ 596 | $ 494 | 398 |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] | | | |
Vesting period | 10 years | | |
Restricted Stock Units (RSUs) [Member] | | | |
Salaries, Wages and Officers' Compensation [Abstract] | | | |
Compensation expense, stock-based compensation | $ | $ 897 | $ 775 | $ 615 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] | | | |
Unvested, beginning balance | shares | 141,985 | | |
Granted | shares | 35,015 | | |
Forfeited | shares | 0 | | |
Vested | shares | (24,521) | | |
Unvested, ending balance | shares | 152,479 | 141,985 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] | | | |
Unvested, weighted average award date value, beginning balance | $ 23.98 | | |
Granted, weighted average award date value | 31.59 | | |
Forfeited, weighted average award date value | 0 | | |
Vested, weighted average award date value | 19.63 | | |
Unvested, weighted average award date value, ending balance | $ 26.43 | $ 23.98 | |
Weighted average remaining contractual life (years) | 2 years 6 months | | |
Unrecognized compensation cost | $ | $ 2,119 | | |
Aggregate intrinsic value, unvested | $ | $ 5,169 | | |
Nonemployee Director SSARs [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] | | | |
Unvested, ending balance | shares | 2,999 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] | | | |
Unvested, weighted average award date value, ending balance | $ 2.03 | | |
Weighted average remaining contractual life (years) | 4 months 24 days | | |
Unrecognized compensation cost | $ | $ 2 | | |
Aggregate intrinsic value, unvested | $ | $ 102 | | |
Employee PRSUs [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] | | | |
Unvested, ending balance | shares | 133,084 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] | | | |
Unvested, weighted average award date value, ending balance | $ 26.09 | | |
Weighted average remaining contractual life (years) | 2 years 8 months 12 days | | |
Unrecognized compensation cost | $ | $ 1,843 | | |
Aggregate intrinsic value, unvested | $ | $ 4,512 | | |
Nonemployee Director PRSUs [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] | | | |
Unvested, ending balance | shares | 19,395 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] | | | |
Unvested, weighted average award date value, ending balance | $ 28.70 | | |
Weighted average remaining contractual life (years) | 1 year 8 months 12 days | | |
Unrecognized compensation cost | $ | $ 276 | | |
Aggregate intrinsic value, unvested | $ | $ 657 | | |