STOCK-BASED COMPENSATION (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) Integer $ / shares shares		Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2013 $ / shares shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 shares	Dec. 31, 2015 shares
Stock Compensation Plan disclosure [Abstract]
Stock-based compensation cost | $	$ 7,012,000		$ 5,831,000	$ 8,423,000
Award Recipient Type Employee [Member] | Restricted Stock [Member]
Stock Compensation Plan disclosure [Abstract]
Stock-based compensation cost | $	6,309,000		5,184,000	7,891,000
Stock based compensation cost capitalized as development costs | $	$ 1,458,000		$ 1,183,000	$ 1,672,000
Share awards granted (in shares)	93,285	[1]	80,529	100,622
Grant date fair value of shares issued (in dollars per share) | $ / shares	$ 76.70	[1]	$ 58.81	$ 61.07
Compensation is recognized over a weighted average period (in years)	2 years 8 months 20 days
Share based compensation, share based payment arrangements other than stock options, unrecognized cost associated with awards not yet vested | $	$ 5,988,000
Shares withheld to satisfy the tax obligations (in shares)	33,695		57,316	32,409
Fair value of shares granted | $	$ 7,155,000		$ 4,736,000	$ 6,145,000
Fair value of shares vested as of the vesting date | $	$ 6,441,000		$ 10,013,000	$ 6,664,000
Restricted Stock Activity [Roll Forward]
Unvested at beginning of year (in shares)	162,087		260,698	265,911
Granted (in shares)	93,285	[1]	80,529	100,622
Forfeited (in shares)	(16,000)		(910)	0
Vested (in shares)	(86,728)		(178,230)	(105,835)
Unvested at end of year (in shares)	152,644		162,087	260,698
Restricted stock activity weighted average price [Abstract]
Unvested at beginning of year (in dollars per share) | $ / shares	$ 51.97		$ 52.68	$ 49.79
Granted (in dollars per share) | $ / shares	76.70	[1]	58.81	61.07
Forfeited (in dollars per share) | $ / shares	36.98		52.89	0.00
Vested (in dollars per share) | $ / shares	61.62		56.09	53.40
Unvested at end of year (in dollars per share) | $ / shares	$ 63.18		$ 51.97	$ 52.68
Nonvested Shares Vesting Schedule [Abstract]
2018 (in shares)						50,158
2019 (in shares)						44,235
2020 (in shares)						41,064
2021 (in shares)						13,584
2022 (in shares)						3,603
Total Nonvested Shares (in shares)	162,087		260,698	265,911		152,644	162,087	260,698
Award Recipient Type Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual Director Retainer Stock Award Amount | $						$ 80,000
Stock Compensation Plan disclosure [Abstract]
Stock-based compensation cost | $	$ 670,000		$ 589,000	$ 514,000
Award Recipient Type Director [Member] | Restricted Stock [Member]
Stock Compensation Plan disclosure [Abstract]
Fair value of shares vested as of the vesting date | $	$ 9,000		$ 8,000	$ 6,000
Management Incentive Plan 2004 [Member]
Stock Compensation Plan disclosure [Abstract]
Authorized shares of common stock (in shares)						1,900,000
Equity Incentive Plan 2013 [Member]
Stock Compensation Plan disclosure [Abstract]
Authorized shares of common stock (in shares)						2,000,000
Shares available for grant (in shares)						1,671,981	1,752,345	1,802,000
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Executive Officer [Member]
Stock Compensation Plan disclosure [Abstract]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (maximum)	59,477
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (minimum)	0
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Company Performance Awards [Member] | Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of vesting that occurred on grant date	20.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)	36,571
Grant date fair value of shares issued (in dollars per share) | $ / shares	$ 74.80
Percentage of shares granted vesting annually in future periods (in hundredths)						20.00%
Restricted Stock Activity [Roll Forward]
Granted (in shares)	36,571
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares	$ 74.80
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of vesting that occurred on grant date	25.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)	33,289
Grant date fair value of shares issued (in dollars per share) | $ / shares	$ 74.80
Percentage of shares granted vesting annually in future periods (in hundredths)						25.00%
Equity Instruments other than options, number of plans | Integer	3
Restricted Stock Activity [Roll Forward]
Granted (in shares)	33,289
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares	$ 74.80
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Service Condition Only Awards [Member] | Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	25.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)	5,406
Grant date fair value of shares issued (in dollars per share) | $ / shares	$ 78.18
Equity Instruments other than options, number of plans | Integer	1
Restricted Stock Activity [Roll Forward]
Granted (in shares)	5,406
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares	$ 78.18
Equity Incentive Plan 2013 [Member] | Award Recipient Type Employee [Member] | Restricted Stock [Member] | Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	20.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)	5,169
Grant date fair value of shares issued (in dollars per share) | $ / shares	$ 81.27
Restricted Stock Activity [Roll Forward]
Granted (in shares)	5,169
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares	$ 81.27
Equity Incentive Plan 2013 [Member] | Award Recipient Type Employee [Member] | Restricted Stock [Member] | Non Executive Officers [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by Share-based payment award, % vesting after grant date and before date report was filed	20.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	20.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)	12,850
Grant date fair value of shares issued (in dollars per share) | $ / shares	$ 84.57
Restricted Stock Activity [Roll Forward]
Granted (in shares)	12,850
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares	$ 84.57
Equity Incentive Plan 2013 [Member] | Award Recipient Type Employee [Member] | Restricted Stock [Member] | Company Performance Awards [Member] | Executive Officer [Member]
Stock Compensation Plan disclosure [Abstract]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (maximum)	21,096
Grant date fair value of shares issued (in dollars per share) | $ / shares	$ 78.18
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (minimum)	0
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on grant date	20.00%
Share Based Compensation Arrangement By Share Based Payment Award Possible Shares To Be Awarded Vesting Rights	20.00%
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares	$ 78.18
Equity Incentive Plan 2013 [Member] | Award Recipient Type Employee [Member] | Restricted Stock [Member] | Individual performance awards [Member] | Executive Officer [Member]
Stock Compensation Plan disclosure [Abstract]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (maximum)	5,274
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (minimum)	0
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on grant date	20.00%
Share Based Compensation Arrangement By Share Based Payment Award Possible Shares To Be Awarded Vesting Rights	20.00%
Equity Incentive Plan 2013 [Member] | Award Recipient Type Director [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)	25.00%				25.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)	282				417
Grant date fair value of shares issued (in dollars per share) | $ / shares	$ 88.86				$ 59.97
Restricted Stock Activity [Roll Forward]
Granted (in shares)	282				417
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares	$ 88.86				$ 59.97
Award Recipient Type Director [Member]
Stock Compensation Plan disclosure [Abstract]
Shares issued to directors (in shares)	8,881		10,072	9,373
New Director Stock Awards to be Issued in Future Periods [Member] | Award Recipient Type Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New Director Restricted Stock Award Amount to be Awarded in Future Periods | $	$ 25,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
One year period [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member]
Stock Compensation Plan disclosure [Abstract]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (maximum)	4,730
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (minimum)	0
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on grant date	100.00%
Stock options exercisable [Abstract]
Number of years in total shareholder return performance period | Integer	1
Two year period [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member]
Stock Compensation Plan disclosure [Abstract]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (maximum)	9,460
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (minimum)	0
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on grant date	100.00%
Stock options exercisable [Abstract]
Number of years in total shareholder return performance period | Integer	2
Three year period [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member]
Stock Compensation Plan disclosure [Abstract]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (maximum)	18,917
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (minimum)	0
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on grant date	75.00%
Share Based Compensation Arrangement By Share Based Payment Award Possible Shares To Be Awarded Vesting Rights	25.00%
Stock options exercisable [Abstract]
Number of years in total shareholder return performance period | Integer	3

[1] Does not include the restricted shares that may be earned if the performance goals established in 2017 for annual and long-term performance periods are achieved. Depending on the actual level of achievement of the goals at the end of the open performance periods, the number of shares earned could range from zero to 59,477.