Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 1,337,973	$ 1,229,162	$ 1,185,097
Direct costs	857,508	771,725	745,137
Operating costs and expenses
Indirect and selling expenses	360,987	346,440	328,048
Depreciation and amortization	17,163	17,691	16,638
Amortization of intangible assets	10,043	10,888	12,481
Total operating costs and expenses	388,193	375,019	357,167
Operating income	92,272	82,418	82,793
Interest expense	(8,710)	(8,553)	(9,470)
Other (expense) income	(735)	121	1,184
Income before income taxes	82,827	73,986	74,507
Provision for income taxes	21,427	11,110	27,923
Net income	$ 61,400	$ 62,876	$ 46,584
Earnings per share:
Basic	$ 3.27	$ 3.35	$ 2.45
Diluted	$ 3.18	$ 3.27	$ 2.40
Weighted-average common shares outstanding:
Basic	18,797	18,766	18,989
Diluted	19,335	19,244	19,416
Cash dividends declared per common share	$ 0.56
Other comprehensive (loss) income, net of tax	$ (6,683)	$ 4,601	$ (2,149)
Comprehensive income, net of tax	$ 54,717	$ 67,477	$ 44,435