DISAGGREGATION OF REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue
Total revenues	$ 283,285	$ 285,746	$ 271,091	$ 276,541	$ 288,837	$ 275,400	$ 275,124	$ 247,066	$ 1,116,663	$ 1,086,427	$ 935,282
Intercompany
Disaggregation of Revenue
Total revenues									(19,131)	(15,496)	(13,155)
Corporate
Disaggregation of Revenue
Total revenues									(19,120)	(9,240)	(8,274)
Corporate and Elimination
Disaggregation of Revenue
Total revenues									(19,120)	(9,240)	(8,274)
Enterprise Software | Intercompany
Disaggregation of Revenue
Total revenues									19,061	15,290	12,764
Enterprise Software | Operating segments
Disaggregation of Revenue
Total revenues									1,020,959	975,319	828,642
Appraisal and Tax | Intercompany
Disaggregation of Revenue
Total revenues									70	206	391
Appraisal and Tax | Operating segments
Disaggregation of Revenue
Total revenues									114,824	120,348	114,914
Recurring revenues
Disaggregation of Revenue
Total revenues									818,160	726,670	605,069
Recurring revenues | Corporate
Disaggregation of Revenue
Total revenues									0	0	0
Recurring revenues | Enterprise Software
Disaggregation of Revenue
Total revenues									755,508	672,804	554,581
Recurring revenues | Appraisal and Tax
Disaggregation of Revenue
Total revenues									62,652	53,866	50,488
Non-recurring revenues
Disaggregation of Revenue
Total revenues									298,503	359,757	330,213
Non-recurring revenues | Corporate
Disaggregation of Revenue
Total revenues									11	6,256	4,881
Non-recurring revenues | Enterprise Software
Disaggregation of Revenue
Total revenues									246,390	287,225	261,297
Non-recurring revenues | Appraisal and Tax
Disaggregation of Revenue
Total revenues									52,102	66,276	64,035
Products and services transferred at a point in time
Disaggregation of Revenue
Total revenues									79,831	107,912	98,846
Products and services transferred over time
Disaggregation of Revenue
Total revenues									1,036,832	978,515	836,436
Software licenses and royalties
Disaggregation of Revenue
Total revenues									73,164	100,205	93,441
Software licenses and royalties | Corporate
Disaggregation of Revenue
Total revenues									0	0	0
Software licenses and royalties | Enterprise Software
Disaggregation of Revenue
Total revenues									64,200	90,808	81,299
Software licenses and royalties | Appraisal and Tax
Disaggregation of Revenue
Total revenues									8,964	9,397	12,142
Software licenses and royalties | Products and services transferred at a point in time
Disaggregation of Revenue
Total revenues									62,029	84,900	75,188
Software licenses and royalties | Products and services transferred over time
Disaggregation of Revenue
Total revenues									11,135	15,305	18,253
Subscriptions
Disaggregation of Revenue
Total revenues									350,648	296,352	220,547
Subscriptions | Corporate
Disaggregation of Revenue
Total revenues									0	0	0
Subscriptions | Enterprise Software
Disaggregation of Revenue
Total revenues									326,284	279,282	205,193
Subscriptions | Appraisal and Tax
Disaggregation of Revenue
Total revenues									24,364	17,070	15,354
Subscriptions | Products and services transferred at a point in time
Disaggregation of Revenue
Total revenues									0	0	0
Subscriptions | Products and services transferred over time
Disaggregation of Revenue
Total revenues									350,648	296,352	220,547
Software services
Disaggregation of Revenue
Total revenues									186,409	213,061	191,269
Software services | Corporate
Disaggregation of Revenue
Total revenues									0	0	0
Software services | Enterprise Software
Disaggregation of Revenue
Total revenues									164,520	179,865	161,612
Software services | Appraisal and Tax
Disaggregation of Revenue
Total revenues									21,889	33,196	29,657
Software services | Products and services transferred at a point in time
Disaggregation of Revenue
Total revenues									0	0	0
Software services | Products and services transferred over time
Disaggregation of Revenue
Total revenues									186,409	213,061	191,269
Maintenance
Disaggregation of Revenue
Total revenues									467,513	430,318	384,521
Maintenance | Corporate
Disaggregation of Revenue
Total revenues									0	0	0
Maintenance | Enterprise Software
Disaggregation of Revenue
Total revenues									429,224	393,521	349,387
Maintenance | Appraisal and Tax
Disaggregation of Revenue
Total revenues									38,289	36,797	35,134
Maintenance | Products and services transferred at a point in time
Disaggregation of Revenue
Total revenues									0	0	0
Maintenance | Products and services transferred over time
Disaggregation of Revenue
Total revenues									467,513	430,318	384,521
Appraisal services
Disaggregation of Revenue
Total revenues									21,127	23,479	21,846
Appraisal services | Corporate
Disaggregation of Revenue
Total revenues									0	0	0
Appraisal services | Enterprise Software
Disaggregation of Revenue
Total revenues									0	0	0
Appraisal services | Appraisal and Tax
Disaggregation of Revenue
Total revenues									21,127	23,479	21,846
Appraisal services | Products and services transferred at a point in time
Disaggregation of Revenue
Total revenues									0	0	0
Appraisal services | Products and services transferred over time
Disaggregation of Revenue
Total revenues									21,127	23,479	21,846
Hardware and other
Disaggregation of Revenue
Total revenues									17,802	23,012	23,658
Hardware and other | Products and services transferred at a point in time
Disaggregation of Revenue
Total revenues									17,802	23,012	23,658
Hardware and other | Products and services transferred over time
Disaggregation of Revenue
Total revenues									$ 0	$ 0	$ 0