Business Combinations, Clarity (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Allocation of Total Purchase Price Consideration [Abstract]
Goodwill	$ 304,583	$ 275,205
Clarity Consultants [Member]
Business Combinations [Abstract]
Date of acquisition	Jun. 22, 2017
Cash paid for acquisition	$ 30,700
Common stock issued	7,300
Net working capital settlement	(500)
Initial fair value estimate of additional earnings-based contingent consideration	$ 4,100
Period to realize additional earnings-based contingent consideration	12 months
Maximum potential additional earnings-based contingent consideration	$ 9,200
Transaction costs	900
Common stock value attributed to future compensation	900
Allocation of Total Purchase Price Consideration [Abstract]
Acquired tangible assets	6,300
Acquired intangible assets	15,400
Liabilities assumed	(3,900)
Goodwill	23,800
Total purchase price	41,600
Tax deductible amount of Goodwill	$ 21,300