Business Combinations - Southport (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Apr. 02, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Business Combinations [Abstract]
Period to realize additional earnings-based contingent consideration				12 months
Adjustment to fair value of contingent consideration		$ 666	$ (389)	$ 1,757	$ (828)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill		321,995		321,995		$ 305,238
Southport Services Group, LLC
Business Combinations [Abstract]
Date of acquisition	Apr. 02, 2018
Cash paid for acquisition	$ 11,300
Common stock issued	2,700
Net working capital settlement	300
Initial fair value estimate of additional earnings-based contingent consideration	4,300
Contingent consideration, maximum cash payout		6,600		6,600
Current Contingent Consideration Liability		5,000		5,000
Adjustment to fair value of contingent consideration		700		700
Transaction costs		800		800
Common stock value attributed to future compensation		300		300
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Acquired tangible assets	4,200
Identified intangible assets	5,700
Liabilities assumed	(1,800)
Goodwill	10,500
Total purchase price	$ 18,600
Tax deductible amount of Goodwill		$ 7,100		$ 7,100