Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenue	$ 1,506,875	$ 1,478,525	$ 1,337,973
Direct costs	972,406	953,187	857,508
Operating costs and expenses
Indirect and selling expenses	411,612	395,763	360,987
Depreciation and amortization	20,399	20,099	17,163
Amortization of intangible assets	13,349	8,083	10,043
Total operating costs and expenses	445,360	423,945	388,193
Operating income	89,109	101,393	92,272
Interest expense	(13,892)	(10,719)	(8,710)
Other expense	(544)	(501)	(735)
Income before income taxes	74,673	90,173	82,827
Provision for income taxes	19,714	21,235	21,427
Net income	$ 54,959	$ 68,938	$ 61,400
Earnings per share:
Basic	$ 2.92	$ 3.66	$ 3.27
Diluted	$ 2.87	$ 3.59	$ 3.18
Weighted-average common shares outstanding:
Basic	18,841	18,816	18,797
Diluted	19,135	19,224	19,335
Cash dividends declared per common share	$ 0.56	$ 0.56	$ 0.56
Other comprehensive (loss) income, net of tax	$ (1,962)	$ 407	$ (6,683)
Comprehensive income, net of tax	$ 52,997	$ 69,345	$ 54,717