CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Revenue	$ 1,710,765	$ 1,579,922	$ 1,397,700
Direct costs	1,209,658	1,123,058	1,001,476
Gross profit	501,107	456,864	396,224
Selling, general and administrative expenses	379,815	345,721	310,713
Depreciation and amortization	4,427	4,500	5,255
Income from operations	116,865	106,643	80,256
Other expense, net	14,423	7,376	5,044
Income from operations, before income taxes	102,442	99,267	75,212
Income tax expense	27,011	24,090	19,173
Net income	75,431	75,177	56,039
Other comprehensive (loss) income:
Defined benefit pension plans, net of tax	0	3,103	(1,706)
Change in fair value of interest rate swap, net of tax	(615)	1,941	(1,191)
Comprehensive income	$ 74,816	$ 80,221	$ 53,142
Earnings per share:
Basic (in dollars per share)	$ 3.76	$ 3.65	$ 2.67
Diluted (in dollars per share)	$ 3.68	$ 3.54	$ 2.62
Weighted average shares outstanding - basic (in shares)	20,054	20,579	20,983
Weighted average shares outstanding – diluted (in shares)	20,503	21,212	21,395