STOCK BENEFIT PLAN (Details 3) (Restricted stock, USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Number of Shares
Restricted stock outstanding and unvested at the beginning of the period (in shares)	289,448
Granted (in shares)	119,604
Vested and issued (in shares)	(107,546)
Cancelled (in shares)	(6,472)
Restricted stock outstanding and unvested at the end of the period (in shares)	295,034	289,448
Weighted Average Grant Date Fair Value Per Share
Restricted stock outstanding and unvested at the beginning of the period (in dollars per share)	$ 50.29
Granted (in dollars per share)	$ 63.62	$ 62.09	$ 49.35
Vested and issued (in dollars per share)	$ 50.39
Cancelled (in dollars per share)	$ 45.05
Restricted stock outstanding and unvested at the end of the period (in dollars per share)	$ 55.77	$ 50.29
Total unrecognized compensation cost related to unvested restricted stock	$ 5,258
Weighted average period for recognition of unrecognized compensation cost	2 years 1 month 20 days
Summary of restricted stock activity
Stock-based compensation costs recognized	7,659	6,226	4,527
Fair value of restricted shares vested	$ 6,707	$ 5,246	$ 3,447
Weighted average price of shares granted (in dollars per share)	$ 63.62	$ 62.09	$ 49.35
Number of restricted shares granted (in shares)	119,604
Eligible employee
Number of Shares
Granted (in shares)	108,065	87,913	108,252
Summary of restricted stock activity
Number of restricted shares granted (in shares)	108,065	87,913	108,252
Non-employee director
Number of Shares
Granted (in shares)	11,539	9,464	12,760
Summary of restricted stock activity
Number of restricted shares granted (in shares)	11,539	9,464	12,760

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph g(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

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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.

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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.

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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.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The total fair value of equity-based awards 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.

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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.

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