UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Revenue	$ 403,614	$ 343,020	$ 766,839	$ 678,228
Direct costs	284,683	245,659	549,226	486,343
Gross profit	118,931	97,361	217,613	191,885
Selling, general and administrative expenses	84,616	80,546	162,645	159,762
Depreciation and amortization	1,192	1,380	2,394	2,773
Income from operations	33,123	15,435	52,574	29,350
Other expense, net	3,112	1,427	4,397	2,808
Income from operations, before income taxes	30,011	14,008	48,177	26,542
Income tax expense	8,823	4,123	13,728	7,551
Net income	21,188	9,885	34,449	18,991
Other comprehensive income (loss), net of tax:
Defined benefit pension plans	3,056	0	3,103	0
Change in fair value of interest rate swaps	10	(470)	949	(1,591)
Comprehensive income	$ 24,254	$ 9,415	$ 38,501	$ 17,400
Earnings per share – basic (in dollars per share)	$ 1.02	$ 0.48	$ 1.66	$ 0.90
Earnings per share - diluted (in dollars per share)	$ 1.00	$ 0.47	$ 1.61	$ 0.89
Weighted average shares outstanding – basic (in shares)	20,673	20,790	20,802	21,171
Weighted average shares outstanding – diluted (in shares)	21,282	21,078	21,331	21,469