CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenue	$ 1,397,700	$ 1,347,387	$ 1,303,937
Direct costs	1,001,476	952,349	917,450
Gross profit	396,224	395,038	386,487
Selling, general and administrative expenses	310,713	314,167	307,250
Depreciation and amortization	5,255	6,050	6,836
Income from operations	80,256	74,821	72,401
Other expense, net	5,044	3,425	4,521
Income from continuing operations, before income taxes	75,212	71,396	67,880
Income tax expense	19,173	16,830	17,004
Income from continuing operations	56,039	54,566	50,876
Income from discontinued operations, net of tax	0	76,296	7,104
Net income	56,039	130,862	57,980
Other comprehensive (loss) income:
Defined benefit pension plans, net of tax	(1,706)	(2,183)	881
Change in fair value of interest rate swap, net of tax	(1,191)	(807)
Change in fair value of interest rate swap, net of tax			315
Comprehensive income	$ 53,142	$ 127,872	$ 59,176
Earnings per share - basic:
Continuing operations (in dollars per share)	$ 2.67	$ 2.35	$ 2.05
Discontinued operations (in dollars per share)	0	3.29	0.29
Earnings per share – basic (in dollars per share)	2.67	5.64	2.34
Earnings per share - diluted:
Continuing operations (in dollars per share)	2.62	2.29	2.02
Discontinued operations (in dollars per share)	0	3.21	0.28
Earnings per share – diluted (in dollars per share)	$ 2.62	$ 5.50	$ 2.30
Weighted average shares outstanding - basic (in shares)	20,983	23,186	24,738
Weighted average shares outstanding – diluted (in shares)	21,395	23,772	25,251