Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue
Total revenues	$ 404,075	$ 271,091	$ 698,877	$ 547,632
Intercompany
Disaggregation of Revenue
Total revenues	(5,621)	(4,535)	(10,897)	(8,554)
Intercompany | Enterprise Software
Disaggregation of Revenue
Total revenues	5,605	4,533	10,866	8,534
Intercompany | Appraisal and Tax
Disaggregation of Revenue
Total revenues	16	2	31	20
Intercompany | NIC
Disaggregation of Revenue
Total revenues	0	0	0	0
Operating segments | Enterprise Software
Disaggregation of Revenue
Total revenues	277,501	247,879	547,109	498,056
Operating segments | Appraisal and Tax
Disaggregation of Revenue
Total revenues	30,177	27,747	60,647	58,128
Operating segments | NIC
Disaggregation of Revenue
Total revenues	99,079	0	99,079	0
Corporate
Disaggregation of Revenue
Total revenues	(2,682)	(4,535)	(7,958)	(8,552)
Corporate and Elimination
Disaggregation of Revenue
Total revenues	(2,682)	(4,535)	(7,958)	(8,552)
Recurring revenues
Disaggregation of Revenue
Total revenues	319,179	202,398	540,770	398,486
Recurring revenues | Enterprise Software
Disaggregation of Revenue
Total revenues	208,417	186,464	413,031	367,949
Recurring revenues | Appraisal and Tax
Disaggregation of Revenue
Total revenues	17,326	15,934	34,303	30,537
Recurring revenues | NIC
Disaggregation of Revenue
Total revenues	93,436	0	93,436	0
Recurring revenues | Corporate
Disaggregation of Revenue
Total revenues	0	0	0	0
Non-recurring revenues
Disaggregation of Revenue
Total revenues	84,896	68,693	158,107	149,146
Non-recurring revenues | Enterprise Software
Disaggregation of Revenue
Total revenues	63,479	56,882	123,212	121,573
Non-recurring revenues | Appraisal and Tax
Disaggregation of Revenue
Total revenues	12,835	11,811	26,313	27,571
Non-recurring revenues | NIC
Disaggregation of Revenue
Total revenues	5,643	0	5,643	0
Non-recurring revenues | Corporate
Disaggregation of Revenue
Total revenues	2,939	0	2,939	2
Software licenses and royalties
Disaggregation of Revenue
Total revenues	17,604	17,025	32,537	35,762
Software licenses and royalties | Enterprise Software
Disaggregation of Revenue
Total revenues	15,779	14,683	28,826	30,634
Software licenses and royalties | Appraisal and Tax
Disaggregation of Revenue
Total revenues	1,825	2,342	3,711	5,128
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	199,558	85,638	302,037	167,361
Subscriptions | Enterprise Software
Disaggregation of Revenue
Total revenues	98,407	79,128	193,238	155,772
Subscriptions | Appraisal and Tax
Disaggregation of Revenue
Total revenues	7,870	6,510	15,518	11,589
Subscriptions | NIC
Disaggregation of Revenue
Total revenues	93,281	0	93,281	0
Subscriptions | Corporate
Disaggregation of Revenue
Total revenues	0	0	0	0
Software services
Disaggregation of Revenue
Total revenues	53,337	43,654	100,977	95,787
Software services | Enterprise Software
Disaggregation of Revenue
Total revenues	42,972	38,899	85,532	83,848
Software services | Appraisal and Tax
Disaggregation of Revenue
Total revenues	4,722	4,755	9,802	11,939
Software services | NIC
Disaggregation of Revenue
Total revenues	5,643	0	5,643	0
Software services | Corporate
Disaggregation of Revenue
Total revenues	0	0	0	0
Maintenance
Disaggregation of Revenue
Total revenues	119,621	116,760	238,733	231,125
Maintenance | Enterprise Software
Disaggregation of Revenue
Total revenues	110,010	107,336	219,793	212,177
Maintenance | Appraisal and Tax
Disaggregation of Revenue
Total revenues	9,456	9,424	18,785	18,948
Maintenance | NIC
Disaggregation of Revenue
Total revenues	155	0	155	0
Maintenance | Corporate
Disaggregation of Revenue
Total revenues	0	0	0	0
Appraisal services
Disaggregation of Revenue
Total revenues	6,265	4,696	12,730	10,459
Appraisal services | Enterprise Software
Disaggregation of Revenue
Total revenues	0	0	0	0
Appraisal services | Appraisal and Tax
Disaggregation of Revenue
Total revenues	6,265	4,696	12,730	10,459
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	7,690	3,318	11,863	7,138
Hardware and other | Enterprise Software
Disaggregation of Revenue
Total revenues	4,728	3,300	8,854	7,091
Hardware and other | Appraisal and Tax
Disaggregation of Revenue
Total revenues	23	18	70	45
Hardware and other | NIC
Disaggregation of Revenue
Total revenues	0	0	0	0
Hardware and other | Corporate
Disaggregation of Revenue
Total revenues	2,939	0	2,939	2
Products and services transferred at a point in time
Disaggregation of Revenue
Total revenues	22,445	17,786	38,676	37,672
Products and services transferred at a point in time | Software licenses and royalties
Disaggregation of Revenue
Total revenues	14,755	14,468	26,813	30,534
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	7,690	3,318	11,863	7,138
Products and services transferred over time
Disaggregation of Revenue
Total revenues	381,630	253,305	660,201	509,960
Products and services transferred over time | Software licenses and royalties
Disaggregation of Revenue
Total revenues	2,849	2,557	5,724	5,228
Products and services transferred over time | Subscriptions
Disaggregation of Revenue
Total revenues	199,558	85,638	302,037	167,361
Products and services transferred over time | Software services
Disaggregation of Revenue
Total revenues	53,337	43,654	100,977	95,787
Products and services transferred over time | Maintenance
Disaggregation of Revenue
Total revenues	119,621	116,760	238,733	231,125
Products and services transferred over time | Appraisal services
Disaggregation of Revenue
Total revenues	6,265	4,696	12,730	10,459
Products and services transferred over time | Hardware and other
Disaggregation of Revenue
Total revenues	$ 0	$ 0	$ 0	$ 0