Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue
Total revenues	$ 459,873	$ 285,746	$ 1,158,750	$ 833,378
Intercompany
Disaggregation of Revenue
Total revenues	(5,143)	(5,166)	(16,040)	(13,720)
Intercompany | Enterprise Software
Disaggregation of Revenue
Total revenues	5,123	5,128	15,989	13,662
Intercompany | Appraisal and Tax
Disaggregation of Revenue
Total revenues	20	38	51	58
Intercompany | NIC
Disaggregation of Revenue
Total revenues	0	0	0	0
Operating segments | Enterprise Software
Disaggregation of Revenue
Total revenues	285,420	261,939	832,529	759,995
Operating segments | Appraisal and Tax
Disaggregation of Revenue
Total revenues	28,923	28,973	89,570	87,101
Operating segments | NIC
Disaggregation of Revenue
Total revenues	150,585	0	249,664	0
Corporate
Disaggregation of Revenue
Total revenues	(5,055)	(5,166)	(13,013)	(13,718)
Corporate and Elimination
Disaggregation of Revenue
Total revenues	(5,055)	(5,166)	(13,013)	(13,718)
Recurring revenues
Disaggregation of Revenue
Total revenues	370,775	207,268	911,545	605,755
Recurring revenues | Enterprise Software
Disaggregation of Revenue
Total revenues	212,517	191,242	625,548	559,191
Recurring revenues | Appraisal and Tax
Disaggregation of Revenue
Total revenues	15,709	16,026	50,012	46,564
Recurring revenues | NIC
Disaggregation of Revenue
Total revenues	142,549	0	235,985	0
Recurring revenues | Corporate
Disaggregation of Revenue
Total revenues	0	0	0	0
Non-recurring revenues
Disaggregation of Revenue
Total revenues	89,098	78,478	247,205	227,623
Non-recurring revenues | Enterprise Software
Disaggregation of Revenue
Total revenues	67,780	65,569	190,992	187,142
Non-recurring revenues | Appraisal and Tax
Disaggregation of Revenue
Total revenues	13,194	12,909	39,507	40,479
Non-recurring revenues | NIC
Disaggregation of Revenue
Total revenues	8,036	0	13,679	0
Non-recurring revenues | Corporate
Disaggregation of Revenue
Total revenues	88	0	3,027	2
Software licenses and royalties
Disaggregation of Revenue
Total revenues	22,673	19,937	55,210	55,699
Software licenses and royalties | Enterprise Software
Disaggregation of Revenue
Total revenues	21,238	17,798	50,064	48,432
Software licenses and royalties | Appraisal and Tax
Disaggregation of Revenue
Total revenues	1,435	2,139	5,146	7,267
Software licenses and royalties | NIC
Disaggregation of Revenue
Total revenues	0	0	0	0
Software licenses and royalties | Corporate
Disaggregation of Revenue
Total revenues	0	0	0	0
Subscriptions
Disaggregation of Revenue
Total revenues	252,942	89,290	554,979	256,651
Subscriptions | Enterprise Software
Disaggregation of Revenue
Total revenues	102,285	82,972	295,523	238,744
Subscriptions | Appraisal and Tax
Disaggregation of Revenue
Total revenues	8,311	6,318	23,829	17,907
Subscriptions | NIC
Disaggregation of Revenue
Total revenues	142,346	0	235,627	0
Subscriptions | Corporate
Disaggregation of Revenue
Total revenues	0	0	0	0
Software services
Disaggregation of Revenue
Total revenues	54,624	47,946	155,601	143,733
Software services | Enterprise Software
Disaggregation of Revenue
Total revenues	41,985	42,640	127,517	126,488
Software services | Appraisal and Tax
Disaggregation of Revenue
Total revenues	4,603	5,306	14,405	17,245
Software services | NIC
Disaggregation of Revenue
Total revenues	8,036	0	13,679	0
Software services | Corporate
Disaggregation of Revenue
Total revenues	0	0	0	0
Maintenance
Disaggregation of Revenue
Total revenues	117,833	117,979	356,566	349,104
Maintenance | Enterprise Software
Disaggregation of Revenue
Total revenues	110,231	108,270	330,024	320,447
Maintenance | Appraisal and Tax
Disaggregation of Revenue
Total revenues	7,399	9,709	26,184	28,657
Maintenance | NIC
Disaggregation of Revenue
Total revenues	203	0	358	0
Maintenance | Corporate
Disaggregation of Revenue
Total revenues	0	0	0	0
Appraisal services
Disaggregation of Revenue
Total revenues	7,146	5,394	19,876	15,853
Appraisal services | Enterprise Software
Disaggregation of Revenue
Total revenues	0	0	0	0
Appraisal services | Appraisal and Tax
Disaggregation of Revenue
Total revenues	7,146	5,394	19,876	15,853
Appraisal services | NIC
Disaggregation of Revenue
Total revenues	0	0	0	0
Appraisal services | Corporate
Disaggregation of Revenue
Total revenues	0	0	0	0
Hardware and other
Disaggregation of Revenue
Total revenues	4,655	5,200	16,518	12,338
Hardware and other | Enterprise Software
Disaggregation of Revenue
Total revenues	4,558	5,131	13,412	12,222
Hardware and other | Appraisal and Tax
Disaggregation of Revenue
Total revenues	9	69	79	114
Hardware and other | NIC
Disaggregation of Revenue
Total revenues	0	0	0	0
Hardware and other | Corporate
Disaggregation of Revenue
Total revenues	88	0	3,027	2
Products and services transferred at a point in time
Disaggregation of Revenue
Total revenues	23,825	21,977	62,501	59,649
Products and services transferred at a point in time | Software licenses and royalties
Disaggregation of Revenue
Total revenues	19,170	16,777	45,983	47,311
Products and services transferred at a point in time | Subscriptions
Disaggregation of Revenue
Total revenues	0	0	0	0
Products and services transferred at a point in time | Software services
Disaggregation of Revenue
Total revenues	0	0	0	0
Products and services transferred at a point in time | Maintenance
Disaggregation of Revenue
Total revenues	0	0	0	0
Products and services transferred at a point in time | Appraisal services
Disaggregation of Revenue
Total revenues	0	0	0	0
Products and services transferred at a point in time | Hardware and other
Disaggregation of Revenue
Total revenues	4,655	5,200	16,518	12,338
Products and services transferred over time
Disaggregation of Revenue
Total revenues	436,048	263,769	1,096,249	773,729
Products and services transferred over time | Software licenses and royalties
Disaggregation of Revenue
Total revenues	3,503	3,160	9,227	8,388
Products and services transferred over time | Subscriptions
Disaggregation of Revenue
Total revenues	252,942	89,290	554,979	256,651
Products and services transferred over time | Software services
Disaggregation of Revenue
Total revenues	54,624	47,946	155,601	143,733
Products and services transferred over time | Maintenance
Disaggregation of Revenue
Total revenues	117,833	117,979	356,566	349,104
Products and services transferred over time | Appraisal services
Disaggregation of Revenue
Total revenues	7,146	5,394	19,876	15,853
Products and services transferred over time | Hardware and other
Disaggregation of Revenue
Total revenues	$ 0	$ 0	$ 0	$ 0