CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Net revenues	$ 1,120,488	$ 1,001,150	$ 1,098,046
Material costs	354,342	315,410	357,771
Personnel costs	397,574	351,191	372,225
Other operating costs	135,630	100,010	135,224
General and administrative expenses	127,752	127,785	131,473
Depreciation and amortization	32,519	34,847	35,925
Income from operations	72,671	71,907	65,428
Interest expense, net	28,864	32,445	34,258
Non-service defined benefit plan expense	667	632	691
Income before income taxes	43,140	38,830	30,479
Provision for income taxes	1,158	638	2,954
Net income	$ 41,982	$ 38,192	$ 27,525
Basic and Diluted Per Common Share Data:
Basic income per share (in dollars per share)	$ 1.09	$ 1.01	$ 0.74
Weighted average shares used to compute basic earnings per common share (in shares)	38,599,300	37,948,796	37,267,188
Diluted income per share (in dollars per share)	$ 1.07	$ 0.99	$ 0.72
Weighted average shares used to compute diluted earnings per common share (in shares)	39,225,616	38,598,330	38,064,617