Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Mar. 31, 2017
LeadLander | Recurring Measurement | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Consideration liability					$ 2.5
RightAnswers
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Consideration liability		$ 2.0
RightAnswers | Recurring Measurement | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Consideration liability				$ 4.0
Settlements - cash earnouts	$ (1.0)
Unearned settlements - cash earnouts		(1.0)
Remaining balance, earnout consideration liability		2.0
Waterfall | Recurring Measurement | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Consideration liability		1.6	$ 1.2
Increase in cash earnout liability		$ 0.4