Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent earn-out	$ 1,885		$ 2,372
Payments related to contingent consideration	487	$ 0
Recurring | Convertible senior note
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible senior note net	171,294		0
Conversable, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent earn-out	$ 1,900		$ 2,400