STOCK-BASED COMPENSATION (Details)		3 Months Ended						9 Months Ended
		Sep. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) $ / shares shares	Mar. 31, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) Integer $ / shares shares	Sep. 30, 2019 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense | $		$ (2,036,000)	$ (2,694,000)	$ (1,781,000)	$ (1,739,000)	$ (2,291,000)	$ (1,447,000)
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Executive Officer [Member]
Weighted Average Grant Date Fair Value [Abstract]
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, Potential Grants in Future Period (maximum)								109,884
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Company Performance Awards [Member] | Executive Officer [Member] | 2020 Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value of shares issued (in dollars per share) | $ / shares								$ 131.36
Weighted Average Grant Date Fair Value [Abstract]
Granted (per share) | $ / shares								$ 131.36
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on performance determination date or future grant date								34.00%
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, Potential Grants in Future Period (maximum)								19,282
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)								33.00%
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member] | 2018 Awards [Member]
Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments other than options, number of plans | Integer								1
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member] | 2017 Awards [Member]
Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments other than options, number of plans | Integer								3
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member] | 2019 Awards [Member]
Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments other than options, number of plans | Integer								1
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member] | 2020 Awards [Member]
Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments other than options, number of plans | Integer								1
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Individual performance awards [Member] | Executive Officer [Member] | 2019 Awards [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 that vested when number of shares determined								20.00%
Grant date fair value of shares issued (in dollars per share) | $ / shares								$ 141.63
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (in shares)								5,860
Weighted Average Grant Date Fair Value [Abstract]
Granted (per share) | $ / shares								$ 141.63
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)								20.00%
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Individual performance awards [Member] | Executive Officer [Member] | 2020 Awards [Member]
Weighted Average Grant Date Fair Value [Abstract]
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on performance determination date or future grant date								34.00%
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, Potential Grants in Future Period (maximum)								4,812
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)								33.00%
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Service Condition Only Awards [Member] | Executive Officer [Member] | 2018 Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value of shares issued (in dollars per share) | $ / shares								$ 95.19
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (in shares)								7,884
Weighted Average Grant Date Fair Value [Abstract]
Granted (per share) | $ / shares								$ 95.19
Equity Instruments other than options, number of plans | Integer								1
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%
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Service Condition Only Awards [Member] | Executive Officer [Member] | 2017 Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
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, Nonvested, Number of Shares [Roll Forward]
Granted (in shares)								5,406
Weighted Average Grant Date Fair Value [Abstract]
Granted (per share) | $ / shares								$ 78.18
Equity Instruments other than options, number of plans | Integer								1
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%
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Service Condition Only Awards [Member] | Executive Officer [Member] | 2019 Awards [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 that vested when number of shares determined								25.00%
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, Nonvested, Number of Shares [Roll Forward]
Granted (in shares)								9,947
Weighted Average Grant Date Fair Value [Abstract]
Granted (per share) | $ / shares								$ 105.97
Equity Instruments other than options, number of plans | Integer								1
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)								25.00%
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Service Condition Only Awards [Member] | Executive Officer [Member] | 2020 Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value of shares issued (in dollars per share) | $ / shares								$ 131.36
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (in shares)								7,217
Weighted Average Grant Date Fair Value [Abstract]
Granted (per share) | $ / shares								$ 131.36
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on performance determination date or future grant date								25.00%
Equity Instruments other than options, number of plans | Integer								1
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)								25.00%
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Annual equity plan [Member] | Executive Officer [Member] | 2019 Awards [Member]
Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments other than options, number of plans | Integer								3
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Annual equity plan [Member] | Executive Officer [Member] | 2020 Awards [Member]
Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments other than options, number of plans | Integer								2
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Company Performance Awards - Part A [Member] | Executive Officer [Member] | 2019 Awards [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 that vested when number of shares determined								20.00%
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, Nonvested, Number of Shares [Roll Forward]
Granted (in shares)								9,162
Weighted Average Grant Date Fair Value [Abstract]
Granted (per share) | $ / shares								$ 105.97
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)								20.00%
Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Company Performance Awards - Part B [Member] | Executive Officer [Member] | 2019 Awards [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 that vested when number of shares determined								20.00%
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, Nonvested, Number of Shares [Roll Forward]
Granted (in shares)								15,990
Weighted Average Grant Date Fair Value [Abstract]
Granted (per share) | $ / shares								$ 122.61
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)								20.00%
Award Recipient Type Employee [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs capitalized as development costs | $		424,000			523,000			$ 1,478,000	$ 1,300,000
Share-based Payment Arrangement, Expense | $		$ 1,945,000			1,739,000			$ 5,617,000	4,752,000
Grant date fair value of shares issued (in dollars per share) | $ / shares	[1],[2]							$ 101.25
Shares withheld for tax obligations								33,963
Fair value of shares vested as of the vesting date | $								$ 10,873,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested at beginning of period (in shares)				131,024				131,024
Granted (in shares)	[1],[2]							69,654
Forfeited (in shares)								(440)
Vested (in shares)								(80,529)
Weighted Average Grant Date Fair Value [Abstract]
Unvested at beginning of period (per share) | $ / shares				$ 82.79				$ 82.79
Granted (per share) | $ / shares	[1],[2]							101.25
Forfeited (per share) | $ / shares								112.14
Vested (per share) | $ / shares								72.24
Unvested at end of period (per share) | $ / shares		$ 100.52						100.52
Award Recipient Type Employee [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Non Executive Officers [Member] | 2020 Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value of shares issued (in dollars per share) | $ / shares								$ 105.30
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (in shares)								12,300
Weighted Average Grant Date Fair Value [Abstract]
Granted (per share) | $ / shares								$ 105.30
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage								20.00%
Award Recipient Type Employees and Directors [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value of shares issued (in dollars per share) | $ / shares	[1],[2]	$ 120.39
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested at beginning of period (in shares)		119,571
Granted (in shares)	[1],[2]	208
Forfeited (in shares)		0
Vested (in shares)		(70)
Unvested at end of period (in shares)		119,709	119,571					119,709
Weighted Average Grant Date Fair Value [Abstract]
Unvested at beginning of period (per share) | $ / shares		$ 100.48
Granted (per share) | $ / shares	[1],[2]	120.39
Forfeited (per share) | $ / shares		0
Vested (per share) | $ / shares		88.86
Unvested at end of period (per share) | $ / shares		$ 100.52	$ 100.48					$ 100.52
Award Recipient Type Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense | $		$ 91,000			$ 1,000			$ 894,000	$ 725,000
Three year period [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member] | 2018 Awards [Member]
Weighted Average Grant Date Fair Value [Abstract]
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on performance determination date or future grant date								75.00%
Share Based Compensation Arrangement By Share Based Payment Award Possible Shares To Be Awarded Vesting Rights								25.00%
Number of years in total shareholder return performance period | Integer								3
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, Potential Grants in Future Period (maximum)								27,087
Three year period [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member] | 2017 Awards [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 that vested when number of shares determined								75.00%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (in shares)								18,917
Weighted Average Grant Date Fair Value [Abstract]
Number of years in total shareholder return performance period | Integer								3
Share Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Rights (% vesting per year in future years)								25.00%
Three year period [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member] | 2019 Awards [Member]
Weighted Average Grant Date Fair Value [Abstract]
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on performance determination date or future grant date								75.00%
Share Based Compensation Arrangement By Share Based Payment Award Possible Shares To Be Awarded Vesting Rights								25.00%
Number of years in total shareholder return performance period | Integer								3
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, Potential Grants in Future Period (maximum)								33,442
Three year period [Member] | Equity Incentive Plan 2013 [Member] | Restricted Stock [Member] | Shareholder Return Awards [Member] | Executive Officer [Member] | 2020 Awards [Member]
Weighted Average Grant Date Fair Value [Abstract]
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Percent of future vesting that will occur on performance determination date or future grant date								75.00%
Share Based Compensation Arrangement By Share Based Payment Award Possible Shares To Be Awarded Vesting Rights								25.00%
Number of years in total shareholder return performance period | Integer								3
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, Potential Grants in Future Period (maximum)								25,261

[1] Does not include the restricted shares that may be earned if the performance goals established in 2018 and 2019 for long-term performance and in 2020 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 109,884.

[2] Includes shares granted in prior years for which performance conditions have been satisfied and the number of shares have been determined.