EQUITY (Details) - USD ($)	12 Months Ended			145 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	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 Options
Exercised (in shares)	(43,053)	(87,378)	(43,034)
Treasury Stock
Shares Repurchased	70,686	37,567	34,293
Aggregate Cost	$ 4,873,000	$ 2,705,000	$ 2,160,000
Aggregate cost to satisfy tax withholdings and exercise obligations	$ 2,775,000	$ 2,705,000	$ 2,160,000
Shares repurchased to satisfy tax withholdings and exercise obligations	38,279	37,567	34,293
Average Repurchase Price (in dollars per share)	$ 72.50	$ 72.01	$ 63.01
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	$ 49,900,000
2004 and 2016 Repurchase Plan
Treasury Stock
Shares Repurchased	32,407
Aggregate Cost	$ 2,195,000
Average Repurchase Price (in dollars per share)	$ 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)	268,875	351,253
Granted (in shares)		5,000
Exercised (in shares)	(43,053)	(87,378)
Outstanding at the end of the period (in shares)	225,822	268,875	351,253
Vested and expected to vest at the end of the period (in shares)	225,554	268,011
Exercisable at the end of the period (in shares)	222,072	248,875
Weighted Avg. Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 38.64	$ 36.55
Granted (in dollars per share)		71.43
Exercised (in dollars per share)	32.70	32.14
Outstanding at the end of the period (in dollars per share)	39.77	38.64	$ 36.55
Vested and expected to vest at the end of the period (in dollars per share)	39.73	38.53
Exercisable at the end of the period (in dollars per share)	$ 39.23	$ 38.05
Weighted Average Remaining Contractual Term
Outstanding	3 years 10 months 24 days	4 years 8 months 12 days
Vested and expected to vest	3 years 10 months 24 days	4 years 8 months 12 days
Exercisable	3 years 9 months 18 days	4 years 6 months
Aggregate Intrinsic Value
Outstanding	$ 9,114,963	$ 10,646,006
Vested and expected to vest	9,112,630	10,640,134
Exercisable	9,082,338	$ 9,998,956
Unamortized stock based compensation
Unamortized stock based compensation	$ 100,000
Weighted-average period for recognition of unamortized stock-based compensation cost	2 years 7 months 6 days
Stock-based compensation, additional disclosures
Weighted-average fair value of options granted (in dollars per share)		$ 30.70
Aggregate intrinsic value of options exercised	$ 1,591,000	$ 3,488,000	$ 1,098,000
Cash proceeds received upon exercise of options	1,060,000	1,999,000	1,621,000
Excess tax benefits from share-based compensation	$ 591,000	1,423,000	513,000
Weighted-average assumptions using Black-Scholes option-pricing model for estimating fair value of each option granted
Risk-free interest rate (as a percent)	1.55%
Expected dividend yield (as a percent)	1.76%
Expected life	6 years 3 months
Expected volatility (as a percent)	51.85%
Stock compensation expense
Stock compensation expense	$ 100,000	900,000	1,400,000
Restricted Stock
Stock-based compensation
Vesting period	4 years
Unamortized stock based compensation
Unamortized stock based compensation	$ 11,200,000
Weighted-average period for recognition of unamortized stock-based compensation cost	2 years 6 months
Stock compensation expense
Stock compensation expense	$ 6,200,000	$ 4,300,000	$ 3,400,000
Shares
Unvested at the beginning of the period (in shares)	218,401	195,143
Granted (in shares)	100,005	93,864	109,318
Forfeited (in shares)	(1,125)	(1,687)
Vested and issued (in shares)	(88,241)	(68,919)
Unvested at the end of the period (in shares)	229,040	218,401	195,143
Weighted Avg. Fair Value
Unvested at the beginning of the period (in dollars per share)	$ 60.60	$ 55.13
Granted (in dollars per share)	73.34	66.26
Forfeited (in dollars per share)	66.44	65.18
Vested and issued (in dollars per share)	58.01	52.70
Unvested at the end of the period (in dollars per share)	$ 67.13	$ 60.60	$ 55.13
2008 Plan | Restricted Stock
Stock-based compensation
Vesting period	4 years