CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 1,418,353	$ 1,357,940	$ 1,319,706
Direct costs	999,745	949,884	911,207
Gross profit	418,608	408,056	408,499
Selling, general and administrative expenses	329,126	331,172	340,742
Depreciation and amortization	7,831	8,255	8,701
Income from operations	81,651	68,629	59,056
Other expense, net	4,498	4,535	3,101
Income before income taxes	77,153	64,094	55,955
Income tax expense	19,173	30,809	23,182
Net income	57,980	33,285	32,773
Other comprehensive income (loss):
Defined benefit pension plans, net of tax	881	(373)	(134)
Change in fair value of interest rate swap, net of tax	315	289	0
Comprehensive income	$ 59,176	$ 33,201	$ 32,639
Earnings per share – basic (in dollars per share)	$ 2.34	$ 1.32	$ 1.26
Earnings per share – diluted (in dollars per share)	$ 2.30	$ 1.30	$ 1.25
Weighted average shares outstanding - basic (in shares)	24,738	25,222	26,099
Weighted average shares outstanding – diluted (in shares)	25,251	25,586	26,274
Dividends declared per share (in dollars per share)	$ 0.60	$ 0.48	$ 0.48