Accounting Standards and Significant Accounting Policies - Adoption of New Accounting Standard (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Statement of Income
Software licenses and royalties	$ 22,776	$ 21,758
Subscriptions	49,028	39,862
Software services	45,939	42,496
Maintenance	93,897	86,307
Appraisal services	5,394	6,612
Hardware and other	4,140	2,694
Total revenues	221,174	199,729
Selling, general and administrative expenses	47,604	42,780
Amortization of customer and trade name intangibles	3,315	3,325
Operating income	38,838	36,831
Income tax provision	1,612	3,872
Net income	$ 37,825	$ 32,769
Earnings per common share:
Basic (USD per share)	$ 1.00	$ 0.89
Diluted (USD per share)	$ 0.95	$ 0.84
Assets
Accounts receivable	$ 216,516		$ 246,188
Prepaid expenses	30,262		32,206
Accounts receivable, long-term	11,550		12,107
Other intangibles, net	221,069		229,617
Total assets	1,625,624		1,611,351
Liabilities
Deferred revenue	268,132		298,613
Deferred income taxes	44,220		46,879
Retained earnings	662,288		624,463
Total liabilities and shareholders' equity	$ 1,625,624		1,611,351
As Reported
Statement of Income
Software licenses and royalties		$ 18,223
Subscriptions		40,102
Software services		45,018
Maintenance		86,859
Appraisal services		6,612
Hardware and other		2,728
Total revenues		199,542
Selling, general and administrative expenses		43,142
Amortization of customer and trade name intangibles		3,458
Operating income		36,149
Income tax provision		3,653
Net income		$ 32,306
Earnings per common share:
Basic (USD per share)		$ 0.88
Diluted (USD per share)		$ 0.83
Assets
Accounts receivable			227,127
Prepaid expenses			27,252
Accounts receivable, long-term			7,536
Other intangibles, net			236,444
Total assets			1,589,592
Liabilities
Deferred revenue			309,461
Deferred income taxes			38,914
Retained earnings			599,821
Total liabilities and shareholders' equity			1,589,592
Accounting Standards Update 2014-09 | Adjustments
Statement of Income
Software licenses and royalties		$ 3,535
Subscriptions		(240)
Software services		(2,522)
Maintenance		(552)
Appraisal services		0
Hardware and other		(34)
Total revenues		187
Selling, general and administrative expenses		(362)
Amortization of customer and trade name intangibles		(133)
Operating income		682
Income tax provision		219
Net income		$ 463
Assets
Accounts receivable			19,061
Prepaid expenses			4,954
Accounts receivable, long-term			4,571
Other intangibles, net			(6,827)
Total assets			21,759
Liabilities
Deferred revenue			(10,848)
Deferred income taxes			7,965
Retained earnings			24,642
Total liabilities and shareholders' equity			$ 21,759