STOCK-BASED COMPENSATION (Details) - USD ($)		3 Months Ended						9 Months Ended
		Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense		$ (2,461,000)	$ (2,893,000)	$ (2,147,000)	$ (2,036,000)	$ (2,694,000)	$ (1,781,000)
Fair value of shares granted, as of the grant dates								$ 7,682,000
Share based compensation arrangement by share-based payment award, Percent of vesting that will occur the following year								25.00%
Share-based compensation arrangement by share-based payment award, Percent vesting at the end of performance period								75.00%
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of shares vested as of the vesting date								$ 10,343,000
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)								118,911
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number		106,212	97,134					106,212		113,403
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value		$ 116.38	$ 111.44					$ 116.38		$ 100.89
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	[1],[2]	9,200						66,623
Grant date fair value of shares issued (in dollars per share)	[1],[2]	$ 168.35						$ 115.30
Forfeited (in shares)		0						0
Forfeited (per share)		$ 0						$ 0
Vested (in shares)		(122)						(73,814)
Vested (per share)		$ 102.30						$ 91.61
Award Recipient Type Employee [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense		$ 2,458,000			1,945,000			$ 6,791,000	$ 5,617,000
Stock-based compensation costs capitalized as development costs		632,000			424,000			$ 1,661,000	1,478,000
Shares withheld for tax obligations								30,252
Award Recipient Type Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense		$ 3,000			$ 91,000			$ 710,000	$ 894,000

[1] Does not include the restricted shares that may be earned if the performance goals established in 2019 and 2020 for long-term performance and in 2021 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 118,911.

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