Acquisitions - Consideration (Details) - USD ($) $ in Thousands								9 Months Ended
	Aug. 21, 2019	May 24, 2019	Apr. 18, 2019	Dec. 12, 2018	Oct. 03, 2018	Jun. 27, 2018	Mar. 21, 2018	Sep. 30, 2019
Kapost
Business Acquisition [Line Items]
Cash		$ 45,000
Holdback		5,000
Contingent consideration		0
Working capital adjustment		(601)
Total consideration		$ 49,399
Cash holdback payable, payment period		12 months
Postup Holdings
Business Acquisition [Line Items]
Cash			$ 34,825
Holdback			175
Contingent consideration			0
Working capital adjustment			0
Total consideration			$ 35,000
Cash holdback payable, payment period			12 months
Adestra
Business Acquisition [Line Items]
Cash				$ 55,242
Holdback				4,432
Contingent consideration				0
Working capital adjustment				0
Total consideration				$ 59,674
Cash holdback payable, payment period				12 months
Rant & Rave
Business Acquisition [Line Items]
Cash					$ 58,470
Holdback					6,500
Contingent consideration					0
Working capital adjustment					(211)
Total consideration					$ 64,759
Cash holdback payable, payment period					12 months
RO Innovation
Business Acquisition [Line Items]
Cash						$ 12,469
Holdback						1,781
Contingent consideration						0
Working capital adjustment						(87)
Total consideration						$ 14,163
Cash holdback payable, payment period						12 months
Future earn out payments						$ 7,500
Earnout consideration liability						$ 0
Earn out payment								$ 1,500
Interfax
Business Acquisition [Line Items]
Cash							$ 35,000
Holdback							5,000
Contingent consideration							0
Working capital adjustment							0
Total consideration							$ 40,000
Cash holdback payable, payment period							18 months
Cimpl
Business Acquisition [Line Items]
Cash	$ 23,071
Holdback	2,600
Contingent consideration	0
Working capital adjustment	0
Total consideration	$ 25,671
Cash holdback payable, payment period	12 months