Business Combinations, Goodwill and Intangible Assets Business Combinations, Goodwill and Intangible Assets - Pro Forma Information - SCIO (Details) - SCIO - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Revenue of SCIO since acquisition	$ 19,205
Revenues, net	231,124	$ 210,263	$ 689,269	$ 615,157
Net income	$ 15,395	$ 19,580	$ 51,666	$ 51,820
Pro-forma earnings per share, basic (in dollars per share)	$ 0.45	$ 0.58	$ 1.50	$ 1.53
Pro-forma earnings per share, diluted (in dollars per share)	$ 0.44	$ 0.56	$ 1.47	$ 1.47