CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Statement [Abstract]
Net revenues	$ 312,033	$ 280,819	$ 573,320	$ 518,289
Material costs	98,433	89,271	184,025	164,441
Personnel costs	110,275	97,549	211,950	187,429
Other operating costs	38,970	32,788	75,138	64,286
General and administrative expenses	35,444	33,110	67,886	64,013
Depreciation and amortization	8,124	8,007	16,079	16,005
Income from operations	20,787	20,094	18,242	22,115
Interest expense, net	7,524	7,152	14,909	14,492
Non-service defined benefit plan expense	160	167	320	334
Income before income taxes	13,103	12,775	3,013	7,289
Provision for income taxes	2,986	2,616	873	460
Net income	$ 10,117	$ 10,159	$ 2,140	$ 6,829
Basic and diluted per common share data:
Basic income per share (in dollars per share)	$ 0.26	$ 0.26	$ 0.05	$ 0.18
Weighted average shares used to compute basic income per share (in shares)	39,089,865	38,647,042	38,946,937	38,458,733
Diluted income per share (in dollars per share)	$ 0.26	$ 0.26	$ 0.05	$ 0.17
Weighted average shares used to compute diluted income per share (in shares)	39,250,735	39,208,155	39,293,775	39,216,725