Fair Value Measurements - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash held as collateral	$ 3,962,000	$ 5,409,000
Remaining contingent consideration	0	(3,680,000)	$ 0
Contact At Once! [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contingent consideration		3,200,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining contingent consideration	0	3,680,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Contingent Earn-Out [Member] | Contact At Once! [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Decrease to contingent earn-out	200,000	4,100,000
Fair value after re-measurement		3,200,000
Cash payments		900,000
Remaining contingent consideration	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Contingent Earn-Out [Member] | Engage Pty Limited [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Decrease to contingent earn-out		900,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Contingent Earn-Out [Member] | Synchronite, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Decrease to contingent earn-out		$ 1,600,000
Remaining contingent consideration	$ 200,000