Accounting Standards and Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable, net	$ 228.1	$ 258.3	$ 226.8
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Typical contract term	3 years
Contract term	1 year
Percentage withheld from progress billings	5.00%
Accounts receivable payment term	30 days
Sales commissions amortization period	3 years	1 year
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Typical contract term	5 years
Contract term	10 years
Percentage withheld from progress billings	20.00%
Accounts receivable payment term	60 days
Sales commissions amortization period	7 years	2 years
Subscription - Hosting Services | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract term	1 year
Subscription - Hosting Services | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract term	10 years
Appraisal services | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract term	1 year
Appraisal services | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract term	3 years
Unbilled Revenues
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable, net	$ 77.1	$ 64.6
Retention Receivable | Unbilled Revenues
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable, net	$ 7.9	$ 7.2