Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenue	$ 1,478,525	$ 1,337,973	$ 1,229,162
Direct costs	953,187	857,508	771,725
Operating costs and expenses
Indirect and selling expenses	395,763	360,987	346,440
Depreciation and amortization	20,099	17,163	17,691
Amortization of intangible assets	8,083	10,043	10,888
Total operating costs and expenses	423,945	388,193	375,019
Operating income	101,393	92,272	82,418
Interest expense	(10,719)	(8,710)	(8,553)
Other (expense) income	(501)	(735)	121
Income before income taxes	90,173	82,827	73,986
Provision for income taxes	21,235	21,427	11,110
Net income	$ 68,938	$ 61,400	$ 62,876
Earnings per share:
Basic	$ 3.66	$ 3.27	$ 3.35
Diluted	$ 3.59	$ 3.18	$ 3.27
Weighted-average common shares outstanding:
Basic	18,816	18,797	18,766
Diluted	19,224	19,335	19,244
Cash dividends declared per common share	$ 0.56	$ 0.56
Other comprehensive income (loss), net of tax	$ 407	$ (6,683)	$ 4,601
Comprehensive income, net of tax	$ 69,345	$ 54,717	$ 67,477