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EQUITY (Details) - USD ($) | 12 Months Ended | 144 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Sep. 18, 2016 | Sep. 19, 2016 | Sep. 30, 2004
Stock-based compensation |  |  |  |  |  |
Number of shares reserved to be granted under the plan | 2,000,000 |  |  |  |  |
Number of shares available for grant | 801,000 |  |  |  |  |
Treasury Stock |  |  |  |  |  |
Shares Repurchased | 171,907 | 234,746 | 70,686 |  |  |
Aggregate Cost | $ 12,437,000 | $ 12,983,000 | $ 4,873,000 |  |  |
Shares repurchased to satisfy tax withholdings and exercise obligations | 141,180 | 32,814 | 38,279 |  |  |
Aggregate cost to satisfy tax withholdings and exercise obligations | $ 10,859,000 | $ 2,348,000 | $ 2,775,000 |  |  |
Average Repurchase Price (in dollars per share) | $ 76.76 | $ 71.54 | $ 72.50 |  |  |
Number of Options |  |  |  |  |  |
Exercised (in shares) | (158,021) | (35,081) | (43,053) |  |  |
Stock-based compensation, additional disclosures |  |  |  |  |  |
Cash proceeds received upon exercise of options | $ 72,000 | $ 1,030,000 | $ 649,000 |  |  |
2004 Repurchase Plan |  |  |  |  |  |
Treasury Stock |  |  |  |  |  |
Authorized amount |  |  |  |  |  | $ 5,000,000
Aggregate Cost |  |  |  | $ 4,100,000 |  |
2016 Repurchase Plan |  |  |  |  |  |
Treasury Stock |  |  |  |  |  |
Authorized amount |  |  |  |  | $ 50,000,000 |
Value of shares available for repurchase | $ 37,700,000 |  |  |  |  |
2004 and 2016 Repurchase Plan |  |  |  |  |  |
Treasury Stock |  |  |  |  |  |
Shares Repurchased | 30,427 | 201,932 | 32,407 |  |  |
Aggregate Cost | $ 1,577,000 | $ 10,636,000 | $ 2,195,000 |  |  |
Average Repurchase Price (in dollars per share) | $ 51.82 | $ 52.67 | $ 64.72 |  |  |
Stock options |  |  |  |  |  |
Stock-based compensation |  |  |  |  |  |
Expiration term | 10 years |  |  |  |  |
Vesting period | 4 years |  |  |  |  |
Number of Options |  |  |  |  |  |
Outstanding at the beginning of the period (in shares) | 200,021 | 225,822 |  |  |  |
Granted (in shares) | 0 | 10,000 |  |  |  |
Exercised (in shares) | (158,021) | (35,801) |  |  |  |
Outstanding at the end of the period (in shares) | 42,000 | 200,021 | 225,822 |  |  |
Vested and expected to vest at the end of the period (in shares) | 42,000 | 200,021 |  |  |  |
Exercisable at the end of the period (in shares) | 33,250 | 187,521 |  |  |  |
Weighted Avg. Exercise Price |  |  |  |  |  |
Outstanding at the beginning of the period (in dollars per share) | $ 41.76 | $ 39.77 |  |  |  |
Granted (in dollars per share) |  | 52.97 |  |  |  |
Exercised (in dollars per share) | 39.95 | 32.29 |  |  |  |
Outstanding at the end of the period (in dollars per share) | 48.61 | 41.76 | $ 39.77 |  |  |
Vested and expected to vest at the end of the period (in dollars per share) | 48.61 | 41.76 |  |  |  |
Exercisable at the end of the period (in dollars per share) | $ 46.76 | $ 40.77 |  |  |  |
Weighted Average Remaining Contractual Term |  |  |  |  |  |
Outstanding | 4 years 1 month 6 days | 3 years 7 months 6 days |  |  |  |
Vested and expected to vest | 4 years 1 month 6 days | 3 years 7 months 6 days |  |  |  |
Exercisable | 3 years | 3 years 7 months 6 days |  |  |  |
Aggregate Intrinsic Value |  |  |  |  |  |
Outstanding | $ 823,515 | $ 2,780,253 |  |  |  |
Vested and expected to vest | 962,840 | 2,780,253 |  |  |  |
Exercisable | 823,515 | $ 2,757,353 |  |  |  |
Unamortized stock based compensation |  |  |  |  |  |
Unamortized stock based compensation | $ 100,000 |  |  |  |  |
Weighted-average period for recognition of unamortized stock-based compensation cost | 2 years 3 months 18 days |  |  |  |  |
Stock-based compensation, additional disclosures |  |  |  |  |  |
Weighted-average fair value of options granted (in dollars per share) |  | $ 13.77 |  |  |  |
Aggregate intrinsic value of options exercised | $ 5,927,000 | $ 936,000 | $ 1,591,000 |  |  |
Cash proceeds received upon exercise of options | 72,000 | $ 1,030,000 | 649,000 |  |  |
Excess tax benefits from share-based compensation |  |  | 591,000 |  |  |
Weighted-average assumptions using Black-Scholes option-pricing model for estimating fair value of each option granted |  |  |  |  |  |
Risk-free interest rate (as a percent) |  | 1.79% |  |  |  |
Expected dividend yield (as a percent) |  | 1.28% |  |  |  |
Expected life |  | 4 years |  |  |  |
Expected volatility (as a percent) |  | 34.01% |  |  |  |
Stock compensation expense |  |  |  |  |  |
Stock compensation expense | $ 100,000 | $ 100,000 | 100,000 |  |  |
Restricted Stock |  |  |  |  |  |
Stock-based compensation |  |  |  |  |  |
Vesting period | 4 years |  |  |  |  |
Unamortized stock based compensation |  |  |  |  |  |
Unamortized stock based compensation | $ 9,000,000 |  |  |  |  |
Weighted-average period for recognition of unamortized stock-based compensation cost | 2 years 6 months |  |  |  |  |
Stock compensation expense |  |  |  |  |  |
Stock compensation expense | $ 6,100,000 | 6,600,000 | 6,200,000 |  |  |
Additional compensation expenses | $ 200,000 | $ 300,000 | $ 100,000 |  |  |
Shares |  |  |  |  |  |
Unvested at the beginning of the period (in shares) | 214,938 | 229,040 |  |  |  |
Granted (in shares) | 111,474 | 95,095 | 100,005 |  |  |
Forfeited (in shares) | (31,327) | (12,074) |  |  |  |
Vested and issued (in shares) | (94,432) | (97,123) |  |  |  |
Unvested at the end of the period (in shares) | 200,653 | 214,938 | 229,040 |  |  |
Weighted Avg. Fair Value |  |  |  |  |  |
Unvested at the beginning of the period (in dollars per share) | $ 68.62 | $ 67.13 |  |  |  |
Granted (in dollars per share) | 59.52 | 68.09 |  |  |  |
Forfeited (in dollars per share) | 66.53 | 69.71 |  |  |  |
Vested and issued (in dollars per share) | 66.27 | 64.01 |  |  |  |
Unvested at the end of the period (in dollars per share) | $ 65.21 | $ 68.62 | $ 67.13 |  |  |

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- Definition Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(3) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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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://fasb.org/us-gaap/role/ref/legacyRef -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=109197908&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://fasb.org/us-gaap/role/ref/legacyRef -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=109197908&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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