Business Combinations - Stone Temple (Details) - USD ($) $ in Thousands		9 Months Ended
	Jul. 16, 2018	Sep. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Period to realize additional earnings-based contingent consideration		12 months
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill		$ 321,995	$ 305,238
Stone Temple Consulting Corporation
Business Acquisition [Line Items]
Date of acquisition	Jul. 16, 2018
Cash paid for acquisition	$ 9,900
Common stock issued	1,200
Net working capital settlement	100
Initial fair value estimate of additional earnings-based contingent consideration	1,200
Contingent consideration, maximum cash payout		2,600
Transaction costs		500
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Acquired tangible assets	2,500
Identified intangible assets	4,600
Liabilities assumed	(1,500)
Goodwill	6,800
Total purchase price	$ 12,400
Tax deductible amount of Goodwill		$ 5,400