CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues [Abstract]
Total revenues	$ 236,067	$ 214,706	$ 693,301	$ 623,198
Cost of revenues:
Total cost of revenues	124,441	110,717	369,594	329,171
Gross profit	111,626	103,989	323,707	294,027
Selling, general and administrative expenses	52,605	44,513	152,471	130,293
Research and development expense	17,050	11,834	45,929	35,307
Amortization of customer and trade name intangibles	4,386	3,360	11,742	10,016
Operating income	37,585	44,282	113,565	118,411
Other income (expense), net	1,041	75	2,198	(216)
Income before income taxes	38,626	44,357	115,763	118,195
Income tax (benefit) provision	(298)	5,521	(147)	14,820
Net income	$ 38,924	$ 38,836	$ 115,910	$ 103,375
Earnings per common share:
Basic (usd per share)	$ 1.00	$ 1.04	$ 3.01	$ 2.78
Diluted (usd per share)	$ 0.96	$ 0.99	$ 2.87	$ 2.63
Software licenses and royalties
Revenues [Abstract]
Total revenues	$ 22,444	$ 22,762	$ 67,620	$ 63,826
Cost of revenues:
Total cost of revenues	957	826	2,939	2,204
Subscriptions
Revenues [Abstract]
Total revenues	58,699	44,352	160,736	124,731
Acquired software
Cost of revenues:
Total cost of revenues	5,897	5,473	17,003	16,243
Software services
Revenues [Abstract]
Total revenues	48,199	46,045	144,812	134,401
Software services, maintenance and subscriptions
Cost of revenues:
Total cost of revenues	111,508	98,036	327,080	287,748
Maintenance
Revenues [Abstract]
Total revenues	96,215	91,847	286,188	266,965
Appraisal services
Revenues [Abstract]
Total revenues	5,544	6,290	16,470	19,268
Cost of revenues:
Total cost of revenues	3,505	4,089	10,854	12,568
Hardware and other
Revenues [Abstract]
Total revenues	4,966	3,410	17,475	14,007
Cost of revenues:
Total cost of revenues	$ 2,574	$ 2,293	$ 11,718	$ 10,408