Deferred Revenue and Performance Obligations (Deferred Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 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	160,881
Recognition of deferred revenue	(191,995)
Balance, end of period	268,773
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	249,104
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	17,497
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	$ 2,172