Acquisitions - Narrative (Details) - USD ($) $ in Thousands			3 Months Ended	6 Months Ended
	Feb. 28, 2019	Feb. 01, 2019	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill			$ 835,911	$ 835,911	$ 753,718
MicroPact and MyCivic
Business Acquisition [Line Items]
Financial advisory and legal fees				900
MicroPact
Business Acquisition [Line Items]
Cash	$ 1,983
Business acquisition consideration	204,200
Payments to acquire business	197,500
Accrued contingent consideration	7,000
Accrued acquisition holdbacks	1,700
Tangible assets acquired	33,200
Liabilities assumed	23,200
Goodwill	83,065
Identifiable intangible assets	$ 118,843
Weighted average useful life (in years)	10 years
Deferred tax liabilities, net	$ 5,766
Business acquisition consideration adjustment				1,000
Revenue, actual			14,600	20,100
Income (loss), actual			$ (3,200)	$ (3,600)
MyCivic
Business Acquisition [Line Items]
Payments to acquire business		$ 3,700