SEGMENT AND RELATED INFORMATION - Schedule of Segment Revenues and Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information
Total revenues	$ 1,592,287	$ 1,116,663	$ 1,086,427
Depreciation and amortization expense	135,624	81,657	76,672
Total segment operating income	180,735	172,926	156,367
Capitalized software expenditures	21,693	5,776	4,804
Capital expenditures	33,919	21,748	38,098
Total assets	4,732,161	2,607,274	2,191,614
Intercompany
Segment Reporting Information
Total revenues	(22,988)	(19,131)	(15,496)
Intercompany | Enterprise Software
Segment Reporting Information
Total revenues	22,921	19,061	15,290
Intercompany | Appraisal and Tax
Segment Reporting Information
Total revenues	67	70	206
Intercompany | NIC
Segment Reporting Information
Total revenues	0	0	0
Operating segments | Enterprise Software
Segment Reporting Information
Total revenues	1,122,073	1,020,959	975,319
Depreciation and amortization expense	69,728	67,411	64,245
Total segment operating income	377,984	337,627	298,305
Capitalized software expenditures	9,041	5,776	4,804
Capital expenditures	19,520	11,099	19,283
Total assets	965,966	847,672	833,203
Operating segments | Appraisal and Tax
Segment Reporting Information
Total revenues	121,258	114,824	120,348
Depreciation and amortization expense	1,491	1,055	970
Total segment operating income	33,524	33,875	33,730
Capitalized software expenditures	0	0	0
Capital expenditures	988	3,823	8,436
Total assets	230,177	94,149	91,343
Operating segments | NIC
Segment Reporting Information
Total revenues	368,917	0	0
Depreciation and amortization expense	38,851	0	0
Total segment operating income	82,305	0	0
Capitalized software expenditures	6,796	0	0
Capital expenditures	3,165	0	0
Total assets	303,146	0	0
Corporate
Segment Reporting Information
Total revenues	(19,961)	(19,120)	(9,240)
Depreciation and amortization expense	25,554	13,191	11,457
Total segment operating income	(222,628)	(144,952)	(123,581)
Capitalized software expenditures	5,856	0	0
Capital expenditures	10,246	6,826	10,379
Total assets	3,232,872	1,665,453	1,267,068
Operating segment and corporate non-segment
Segment Reporting Information
Total segment operating income	271,185	226,550	208,454
Software licenses and royalties
Segment Reporting Information
Total revenues	74,452	73,164	100,205
Software licenses and royalties | Enterprise Software
Segment Reporting Information
Total revenues	68,101	64,200	90,808
Software licenses and royalties | Appraisal and Tax
Segment Reporting Information
Total revenues	6,351	8,964	9,397
Software licenses and royalties | NIC
Segment Reporting Information
Total revenues	0	0	0
Software licenses and royalties | Corporate
Segment Reporting Information
Total revenues	0	0	0
Subscriptions
Segment Reporting Information
Total revenues	784,435	350,648	296,352
Subscriptions | Enterprise Software
Segment Reporting Information
Total revenues	406,494	326,284	279,282
Subscriptions | Appraisal and Tax
Segment Reporting Information
Total revenues	33,249	24,364	17,070
Subscriptions | NIC
Segment Reporting Information
Total revenues	344,692	0	0
Subscriptions | Corporate
Segment Reporting Information
Total revenues	0	0	0
Software services
Segment Reporting Information
Total revenues	209,391	186,409	213,061
Software services | Enterprise Software
Segment Reporting Information
Total revenues	167,065	164,520	179,865
Software services | Appraisal and Tax
Segment Reporting Information
Total revenues	18,661	21,889	33,196
Software services | NIC
Segment Reporting Information
Total revenues	23,665	0	0
Software services | Corporate
Segment Reporting Information
Total revenues	0	0	0
Maintenance
Segment Reporting Information
Total revenues	474,287	467,513	430,318
Maintenance | Enterprise Software
Segment Reporting Information
Total revenues	438,726	429,224	393,521
Maintenance | Appraisal and Tax
Segment Reporting Information
Total revenues	35,001	38,289	36,797
Maintenance | NIC
Segment Reporting Information
Total revenues	560	0	0
Maintenance | Corporate
Segment Reporting Information
Total revenues	0	0	0
Appraisal services
Segment Reporting Information
Total revenues	27,788	21,127	23,479
Appraisal services | Enterprise Software
Segment Reporting Information
Total revenues	0	0	0
Appraisal services | Appraisal and Tax
Segment Reporting Information
Total revenues	27,788	21,127	23,479
Appraisal services | NIC
Segment Reporting Information
Total revenues	0	0	0
Appraisal services | Corporate
Segment Reporting Information
Total revenues	0	0	0
Hardware and other
Segment Reporting Information
Total revenues	21,934	17,802	23,012
Hardware and other | Enterprise Software
Segment Reporting Information
Total revenues	18,766	17,670	16,553
Hardware and other | Appraisal and Tax
Segment Reporting Information
Total revenues	141	121	203
Hardware and other | NIC
Segment Reporting Information
Total revenues	0	0	0
Hardware and other | Corporate
Segment Reporting Information
Total revenues	$ 3,027	$ 11	$ 6,256