STOCK-BASED COMPENSATION (Details)		3 Months Ended	12 Months Ended
		Sep. 30, 2017 $ / shares shares	Dec. 31, 2019 USD ($) Integer $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2013 $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 shares	Dec. 31, 2017 shares
Stock Compensation Plan disclosure [Abstract]
Stock-based compensation cost | $			$ 9,374,000	$ 6,103,000	$ 7,012,000
Award Recipient Type Employee [Member] | Restricted Stock [Member]
Stock Compensation Plan disclosure [Abstract]
Stock-based compensation cost | $			8,647,000	5,322,000	6,309,000
Stock based compensation cost capitalized as development costs | $			$ 2,536,000	$ 1,173,000	$ 1,458,000
Share awards granted (in shares)	[1]		59,943	50,217	93,285
Grant date fair value of shares issued (in dollars per share) | $ / shares	[1]		$ 94.62	$ 84.09	$ 76.70
Compensation is recognized over a weighted average period (in years)			2 years 8 months 12 days
Share based compensation, share based payment arrangements other than stock options, unrecognized cost associated with awards not yet vested | $			$ 4,556,000
Shares withheld to satisfy the tax obligations (in shares)			28,955	23,824	33,695
Fair value of shares granted | $			$ 5,672,000	$ 4,223,000	$ 7,155,000
Fair value of shares vested as of the vesting date | $			$ 6,662,000	$ 5,142,000	$ 6,441,000
Restricted Stock Activity [Roll Forward]
Unvested at beginning of year (in shares)			143,314	152,644	162,087
Granted (in shares)	[1]		59,943	50,217	93,285
Forfeited (in shares)			3,010	0	16,000
Vested (in shares)			(69,363)	(59,547)	(86,728)
Unvested at end of year (in shares)			130,884	143,314	152,644
Restricted stock activity weighted average price [Abstract]
Unvested at beginning of year (in dollars per share) | $ / shares			$ 70.26	$ 63.18	$ 51.97
Granted (in dollars per share) | $ / shares	[1]		94.62	84.09	76.70
Forfeited (in dollars per share) | $ / shares			86.19	0	36.98
Vested (in dollars per share) | $ / shares			66.99	63.77	61.62
Unvested at end of year (in dollars per share) | $ / shares			$ 82.78	$ 70.26	$ 63.18
Nonvested Shares Vesting Schedule [Abstract]
2020 (in shares)							63,931
2021 (in shares)							30,897
2022 (in shares)							21,934
2023 (in shares)							12,152
2024 (in shares)							1,970
Total Nonvested Shares (in shares)			130,884	152,644	152,644		130,884	143,314	152,644
Award Recipient Type Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual Director Retainer Stock Award Amount | $							$ 90,000
Stock Compensation Plan disclosure [Abstract]
Stock-based compensation cost | $			$ 727,000	$ 1,134,000	$ 670,000
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	$ 7,000	$ 9,000
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)							1,583,223	1,629,281	1,671,981
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)			113,305
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] | 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, Award Vesting Rights, Percentage			20.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)			10,175
Grant date fair value of shares issued (in dollars per share) | $ / shares			$ 112.14
Restricted Stock Activity [Roll Forward]
Granted (in shares)			10,175
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares			$ 112.14
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)			6,384	8,478	8,881
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
2017 Awards [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member]
Stock Compensation Plan disclosure [Abstract]
Equity Instruments other than options, number of plans | Integer			3
2017 Awards [Member] | 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%
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)			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
2017 Awards [Member] | One year period [Member] | 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			100.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)			4,257
Restricted Stock Activity [Roll Forward]
Granted (in shares)			4,257
Nonvested Shares Vesting Schedule [Abstract]
Number of years in total shareholder return performance period | Integer			1
2017 Awards [Member] | Two year period [Member] | 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			100.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)			9,460
Restricted Stock Activity [Roll Forward]
Granted (in shares)			9,460
Nonvested Shares Vesting Schedule [Abstract]
Number of years in total shareholder return performance period | Integer			2
2017 Awards [Member] | 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%
Nonvested Shares Vesting Schedule [Abstract]
Number of years in total shareholder return performance period | Integer			3
2018 Awards [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member]
Stock Compensation Plan disclosure [Abstract]
Equity Instruments other than options, number of plans | Integer			1
2018 Awards [Member] | 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%
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)			25.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)			7,884
Grant date fair value of shares issued (in dollars per share) | $ / shares			$ 95.19
Equity Instruments other than options, number of plans | Integer			1
Restricted Stock Activity [Roll Forward]
Granted (in shares)			7,884
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares			$ 95.19
2018 Awards [Member] | Equity Incentive Plan 2013 [Member] | Award Recipient Type Employee [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, Award Vesting Rights, Percentage			20.00%
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)			24,690
Grant date fair value of shares issued (in dollars per share) | $ / shares			$ 95.19
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares			$ 95.19
2018 Awards [Member] | Equity Incentive Plan 2013 [Member] | Award Recipient Type Employee [Member] | Restricted Stock [Member] | Individual 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, Award Vesting Rights, Percentage			20.00%
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-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other Than Options, Potential Grants in Future Period (maximum)			5,671
Grant date fair value of shares issued (in dollars per share) | $ / shares			$ 107.37
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares			$ 107.37
2018 Awards [Member] | 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)			27,596
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%
Nonvested Shares Vesting Schedule [Abstract]
Number of years in total shareholder return performance period | Integer			3
2019 Awards [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Company Performance Awards - Part A [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, Vesting Rights (% vesting per year in future years)			20.00%
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)			9,594
Grant date fair value of shares issued (in dollars per share) | $ / shares			$ 105.97
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%
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares			$ 105.97
2019 Awards [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Company Performance Awards - Part B [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, Vesting Rights (% vesting per year in future years)			20.00%
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)			15,992
Grant date fair value of shares issued (in dollars per share) | $ / shares			$ 122.61
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%
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares			$ 122.61
2019 Awards [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Individual 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, Vesting Rights (% vesting per year in future years)			20.00%
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)			6,394
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%
2019 Awards [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member]
Stock Compensation Plan disclosure [Abstract]
Equity Instruments other than options, number of plans | Integer			1
2019 Awards [Member] | 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, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)			25.00%
Stock Compensation Plan disclosure [Abstract]
Share awards granted (in shares)			9,947
Grant date fair value of shares issued (in dollars per share) | $ / shares			$ 105.97
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on grant date			25.00%
Equity Instruments other than options, number of plans | Integer			1
Restricted Stock Activity [Roll Forward]
Granted (in shares)			9,947
Restricted stock activity weighted average price [Abstract]
Granted (in dollars per share) | $ / shares			$ 105.97
2019 Awards [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Annual equity plan [Member] | Executive Officer [Member]
Stock Compensation Plan disclosure [Abstract]
Equity Instruments other than options, number of plans | Integer			3
2019 Awards [Member] | 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)			34,812
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%
Nonvested Shares Vesting Schedule [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 and 2018 for long-term performance and in 2019 for annual and long-term performance 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 113,305.