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EQUITY (Details) - USD ($) | 12 Months Ended | 145 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | 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 |  |  |  |  |
Treasury Stock |  |  |  |  |  |
Shares Repurchased | 234,746 | 70,686 | 37,567 |  |  |
Aggregate Cost | $ 12,983,000 | $ 4,873,000 | $ 2,705,000 |  |  |
Shares repurchased to satisfy tax withholdings and exercise obligations | 32,814 | 38,279 | 37,567 |  |  |
Aggregate cost to satisfy tax withholdings and exercise obligations | $ 2,348,000 | $ 2,775,000 | $ 2,705,000 |  |  |
Average Repurchase Price (in dollars per share) | $ 71.54 | $ 72.50 | $ 72.01 |  |  |
Number of Options |  |  |  |  |  |
Exercised (in shares) | (35,081) | (43,053) | (87,378) |  |  |
Stock-based compensation, additional disclosures |  |  |  |  |  |
Cash proceeds received upon exercise of options | $ 1,030,000 | $ 649,000 | $ 1,998,000 |  |  |
2004 Repurchase Plan |  |  |  |  |  |
Treasury Stock |  |  |  |  |  |
Authorized amount |  |  |  |  |  | $ 5,000,000
Shares Repurchased |  |  |  | 4,100,000 |  |
2016 Repurchase Plan |  |  |  |  |  |
Treasury Stock |  |  |  |  |  |
Authorized amount |  |  |  |  | $ 50,000,000 |
Value of shares available for repurchase | $ 39,300,000 |  |  |  |  |
2004 and 2016 Repurchase Plan |  |  |  |  |  |
Treasury Stock |  |  |  |  |  |
Shares Repurchased | 201,932 | 32,407 |  |  |  |
Aggregate Cost | $ 10,636,000 | $ 2,195,000 |  |  |  |
Average Repurchase Price (in dollars per share) | $ 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) | 225,822 | 268,875 |  |  |  |
Granted (in shares) | 10,000 |  |  |  |  |
Exercised (in shares) | (35,801) | (43,053) |  |  |  |
Outstanding at the end of the period (in shares) | 200,021 | 225,822 | 268,875 |  |  |
Vested and expected to vest at the end of the period (in shares) | 200,021 | 225,554 |  |  |  |
Exercisable at the end of the period (in shares) | 187,521 | 222,072 |  |  |  |
Weighted Avg. Exercise Price |  |  |  |  |  |
Outstanding at the beginning of the period (in dollars per share) | $ 39.77 | $ 38.64 |  |  |  |
Granted (in dollars per share) | 52.97 |  |  |  |  |
Exercised (in dollars per share) | 32.29 | 32.70 |  |  |  |
Outstanding at the end of the period (in dollars per share) | 41.76 | 39.77 | $ 38.64 |  |  |
Vested and expected to vest at the end of the period (in dollars per share) | 41.76 | 39.73 |  |  |  |
Exercisable at the end of the period (in dollars per share) | $ 40.77 | $ 39.23 |  |  |  |
Weighted Average Remaining Contractual Term |  |  |  |  |  |
Outstanding | 3 years 7 months 6 days | 3 years 10 months 24 days |  |  |  |
Vested and expected to vest | 3 years 7 months 6 days | 3 years 10 months 24 days |  |  |  |
Exercisable | 3 years 7 months 6 days | 3 years 9 months 18 days |  |  |  |
Aggregate Intrinsic Value |  |  |  |  |  |
Outstanding | $ 2,780,253 | $ 9,114,963 |  |  |  |
Vested and expected to vest | 2,780,253 | 9,112,630 |  |  |  |
Exercisable | 2,757,353 | 9,082,338 |  |  |  |
Unamortized stock based compensation |  |  |  |  |  |
Unamortized stock based compensation | $ 200,000 |  |  |  |  |
Weighted-average period for recognition of unamortized stock-based compensation cost | 3 years |  |  |  |  |
Stock-based compensation, additional disclosures |  |  |  |  |  |
Weighted-average fair value of options granted (in dollars per share) | $ 13.77 |  | $ 30.70 |  |  |
Aggregate intrinsic value of options exercised | $ 936,000 | 1,591,000 | $ 3,488,000 |  |  |
Cash proceeds received upon exercise of options | $ 1,030,000 | 649,000 | 1,998,000 |  |  |
Excess tax benefits from share-based compensation |  | 591,000 | $ 1,423,000 |  |  |
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% |  | 1.55% |  |  |
Expected dividend yield (as a percent) | 1.28% |  | 1.76% |  |  |
Expected life | 4 years |  | 6 years 3 months |  |  |
Expected volatility (as a percent) | 34.01% |  | 51.85% |  |  |
Stock compensation expense |  |  |  |  |  |
Stock compensation expense | $ 100,000 | 100,000 | $ 400,000 |  |  |
Restricted Stock |  |  |  |  |  |
Stock-based compensation |  |  |  |  |  |
Vesting period | 4 years |  |  |  |  |
Unamortized stock based compensation |  |  |  |  |  |
Unamortized stock based compensation | $ 10,200,000 |  |  |  |  |
Weighted-average period for recognition of unamortized stock-based compensation cost | 2 years 4 months 24 days |  |  |  |  |
Stock compensation expense |  |  |  |  |  |
Stock compensation expense | $ 6,600,000 | 6,200,000 | 4,300,000 |  |  |
Additional compensation expenses | $ 300,000 | $ 100,000 | $ 300,000 |  |  |
Shares |  |  |  |  |  |
Unvested at the beginning of the period (in shares) | 229,040 | 218,401 |  |  |  |
Granted (in shares) | 95,095 | 100,005 | 93,864 |  |  |
Forfeited (in shares) | (12,074) | (1,125) |  |  |  |
Vested and issued (in shares) | (97,123) | (88,241) |  |  |  |
Unvested at the end of the period (in shares) | 214,938 | 229,040 | 218,401 |  |  |
Weighted Avg. Fair Value |  |  |  |  |  |
Unvested at the beginning of the period (in dollars per share) | $ 67.13 | $ 60.60 |  |  |  |
Granted (in dollars per share) | 68.09 | 73.34 |  |  |  |
Forfeited (in dollars per share) | 69.71 | 66.44 |  |  |  |
Vested and issued (in dollars per share) | 64.01 | 58.01 |  |  |  |
Unvested at the end of the period (in dollars per share) | $ 68.62 | $ 67.13 | $ 60.60 |  |  |
2008 Plan | Restricted Stock |  |  |  |  |  |
Stock-based compensation |  |  |  |  |  |
Vesting period | 4 years |  |  |  |  |

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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (a)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting 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 (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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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://www.xbrl.org/2003/role/presentationRef -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=96867065&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://www.xbrl.org/2003/role/presentationRef -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=96867065&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://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + 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 (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + 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://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting 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 (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement. + 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 (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=96867065&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://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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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + 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 (a)(3) -URI http://asc.fasb.org/extlink&oid=96867065&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://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=96867065&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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&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://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + Details
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