CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (13,124)	$ 9,284	$ (31,893)	$ 14,891	$ 19,808
Other comprehensive income (loss), net of tax:
Change in foreign currency translation adjustments	(202)	143	(57)	26	(85)
Pension benefit plan	421	153	2,989	(495)	(980)
Total comprehensive income (loss)	$ (12,905)	$ 9,580	$ (28,961)	$ 14,422	$ 18,743