Deferred Revenue and Performance Obligations - Deferred Revenue (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Jan. 01, 2017
Disaggregation of Revenue [Line Items]
Deferred revenue	$ 299,887	$ 290,100
Contract With Customer Liability [Roll Forward]
Balance, beginning of period December 31, 2017 (As Adjusted)	299,887
Deferral of revenue	649,152
Recognition of deferred revenue	(622,125)
Balance, end of period	326,914
Operating segments | Enterprise Software
Disaggregation of Revenue [Line Items]
Deferred revenue	277,198
Contract With Customer Liability [Roll Forward]
Balance, beginning of period December 31, 2017 (As Adjusted)	277,198
Balance, end of period	307,872
Operating segments | Appraisal and Tax
Disaggregation of Revenue [Line Items]
Deferred revenue	20,387
Contract With Customer Liability [Roll Forward]
Balance, beginning of period December 31, 2017 (As Adjusted)	20,387
Balance, end of period	16,450
Corporate
Disaggregation of Revenue [Line Items]
Deferred revenue	2,302
Contract With Customer Liability [Roll Forward]
Balance, beginning of period December 31, 2017 (As Adjusted)	2,302
Balance, end of period	$ 2,592