STOCK-BASED COMPENSATION PLAN (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares in the aggregate that may be issued under the 1997 Stock-Based Compensation Plan	2,000,000
Actual amount of shares that ultimately vest of the original share units granted, minimum	0.00%
Actual amount of shares that ultimately vest of the original share units granted, maximum	150.00%
Fair value per share (in dollars per share)	$ 51.292		$ 44.112
Expected volatility, measurement period	3 years
Net Expense	$ 2,761,000		$ 2,292,000	$ 1,820,000
Capitalized	(231,000)		(218,000)	(202,000)
Unrecognized compensation cost of awards granted under the plan	2,300,000
Weighted average period over which unrecognized compensation cost is to be recognized (in years)	1 year 7 months 6 days
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-beginning balance	$ 44.112
Weighted average fair value nonvested shares-granted during the period	$ 54.567
Weighted average fair value nonvested shares-vested during the period	$ 39.670	[1]
Weighted average fair value nonvested shares-cancelled/forfeited during the period	$ 49.430
Weighted average fair value nonvested shares-ending balance	$ 51.292		$ 44.112
Cost [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Net Expense	2,992,000		2,510,000	2,022,000
Officers and Key Employees [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted during the period, Officers & Key Employees	40,955		40,711	52,940
Vesting period of shares	3 years		3 years	3 years
The range of the actual amount of shares that ultimately vest of the original share units granted (in hundredths)	0% to 150%
Shares outstanding (in shares)	81,005		92,907
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested shares outstanding, beginning balance (in shares)	92,907
Granted (in shares)	40,955		40,711	52,940
Vested (in shares)	(52,404)	[1]
Cancelled/Forfeited (in shares)	(453)
Nonvested shares outstanding, ending balance (in shares)	81,005		92,907
Additional disclosures [Abstract]
Shares expected to be awarded to officers and key employees	66,077
Number of shares awarded during the period	33,322		69,271	59,893
Market value of shares awarded	1,900,000		3,700,000	2,300,000
Officers and Key Employees [Member] | Cost [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Net Expense	2,096,000		1,852,000	1,628,000
Officers and Key Employees [Member] | Jan. 2011 - TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	40,227
Fair value per share (in dollars per share)	$ 50.940
Expected volatility	27.50%
Risk-free interest rate	1.01%
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested shares outstanding, ending balance (in shares)	40,227
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 50.940
Officers and Key Employees [Member] | Jan. 2012 - TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	20,389
Fair value per share (in dollars per share)	$ 51.230
Expected volatility	22.50%
Risk-free interest rate	0.43%
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested shares outstanding, ending balance (in shares)	20,389
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 51.230
Officers and Key Employees [Member] | Jan. 2012 - EPS [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	20,389
Fair value per share (in dollars per share)	$ 56.930
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested shares outstanding, ending balance (in shares)	20,389
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 56.930
Directors [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted during the period, Officers & Key Employees	9,904		12,220	16,700
Vesting period of shares	12 months		3 years	3 years
Percent of shares vested, Directors	100.00%
Shares outstanding (in shares)	27,688		21,914
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested shares outstanding, beginning balance (in shares)	21,914
Granted (in shares)	9,904		12,220	16,700
Vested (in shares)	(4,130)	[1]
Cancelled/Forfeited (in shares)	0
Nonvested shares outstanding, ending balance (in shares)	27,688		21,914
Additional disclosures [Abstract]
Market value of shares awarded	600,000		600,000	600,000
Directors [Member] | Cost [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Net Expense	$ 896,000		$ 658,000	$ 394,000
Directors [Member] | Jan. 2010 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	11,690
Fair value per share (in dollars per share)	$ 37.825
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested shares outstanding, ending balance (in shares)	11,690
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 37.825
Directors [Member] | Jan. 2011 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	7,332
Fair value per share (in dollars per share)	$ 52.940
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested shares outstanding, ending balance (in shares)	7,332
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 52.940
Directors [Member] | Jan. 2012 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	8,666
Fair value per share (in dollars per share)	$ 56.580
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested shares outstanding, ending balance (in shares)	8,666
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 56.580

[1] Actual shares expected to be awarded to officers and other key employees during the first quarter of 2013, including dividend equivalents and adjustments for performance measures, total 66,077 shares.