STOCK-BASED COMPENSATION PLAN (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 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		2,000,000
Fair value per share	$ 42.901		$ 42.901
Cost	$ 793,000	$ 518,000	$ 1,389,000	$ 1,036,000
Capitalized	(55,000)	(50,000)	(110,000)	(101,000)
Net expense	738,000	468,000	1,279,000	935,000
Unrecognized compensation cost of awards granted under the plan		3,700,000		3,700,000
Weighted average period over which unrecognized compensation cost is to be recognized (in years)		2.0
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-beginning balance			$ 39.049
Weighted average fair value nonvested shares-granted during the period			$ 51.407
Weighted average fair value nonvested shares-vested during the period			$ 43.300
Weighted average fair value nonvested shares-ending balance	$ 42.901		$ 42.901
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			40,711	52,940
Vesting period of shares			3Y	3Y
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)	131,399		131,399
Number of shares awarded during the period			69,271	59,893
Market value of shares awarded			3,700,000	2,300,000
Cost	466,000	407,000	932,000	814,000
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested shares outstanding, beginning balance			90,688
Granted (in shares)			40,711	52,940
Vested (in shares)			0
Nonvested shares outstanding, ending balance	131,399		131,399
Officers and Key Employees [Member] | Grant Date January 2009 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	37,748		37,748
Fair value per share	$ 39.350		$ 39.350
Expected volatility (in hundredths)			28.60%
Risk-free interest rate (in hundredths)			1.20%
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested shares outstanding, ending balance	37,748		37,748
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 39.350		$ 39.350
Officers and Key Employees [Member] | Grant Date January 2010 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	52,940		52,940
Fair value per share	$ 39.020		$ 39.020
Expected volatility (in hundredths)			29.00%
Risk-free interest rate (in hundredths)			1.65%
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested shares outstanding, ending balance	52,940		52,940
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 39.020		$ 39.020
Officers and Key Employees [Member] | Grant Date January 2011 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	40,711		40,711
Fair value per share	$ 50.940		$ 50.940
Expected volatility (in hundredths)			27.50%
Risk-free interest rate (in hundredths)			1.01%
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested shares outstanding, ending balance	40,711		40,711
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 50.940		$ 50.940
Director [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted during the period, Officers & Key Employees			12,220	16,700
Shares Vested, Directors (in hundredths)	100.00%		100.00%
Shares outstanding (in shares)	30,088		30,088
Number of shares awarded during the period			12,220	16,700
Market value of shares awarded			600,000	600,000
Cost	$ 327,000	$ 111,000	$ 457,000	$ 222,000
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested shares outstanding, beginning balance			25,390
Granted (in shares)			12,220	16,700
Vested (in shares)			(7,522)
Nonvested shares outstanding, ending balance	30,088		30,088
Director [Member] | Grant Date January 2009 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	6,952		6,952
Fair value per share	$ 40.265		$ 40.265
Expected volatility (in hundredths)			0.00%
Risk-free interest rate (in hundredths)			0.00%
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested shares outstanding, ending balance	6,952		6,952
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 40.265		$ 40.265
Director [Member] | Grant Date January 2010 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	13,360		13,360
Fair value per share	$ 37.825		$ 37.825
Expected volatility (in hundredths)			0.00%
Risk-free interest rate (in hundredths)			0.00%
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested shares outstanding, ending balance	13,360		13,360
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 37.825		$ 37.825
Director [Member] | Grant Date January 2011 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	8,554		8,554
Fair value per share	$ 52.940		$ 52.940
Expected volatility (in hundredths)			0.00%
Risk-free interest rate (in hundredths)			0.00%
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested shares outstanding, ending balance	8,554		8,554
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 52.940		$ 52.940
Director [Member] | June 2011 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	1,222		1,222
Fair value per share	$ 53.170		$ 53.170
Expected volatility (in hundredths)			0.00%
Risk-free interest rate (in hundredths)			0.00%
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested shares outstanding, ending balance	1,222		1,222
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance	$ 53.170		$ 53.170