STOCKHOLDERS' EQUITY - AOCI components (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances	$ 828,593	$ 763,043	$ 717,682
OTHER COMPREHENSIVE INCOME, net of tax	2,509	987	14,441
Balances	929,067	828,593	763,043
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances	1,190	203	(14,238)
Other comprehensive income (loss) before reclassifications	2,909	1,359
Amounts reclassified from accumulated other comprehensive income (loss)	(400)	(372)
OTHER COMPREHENSIVE INCOME, net of tax	2,509	987	14,441
Balances	3,699	1,190	203
Unrecognized Net Periodic Benefit Credit
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances	3,260	2,152
Other comprehensive income (loss) before reclassifications	1,300	1,480
Amounts reclassified from accumulated other comprehensive income (loss)	(400)	(372)
OTHER COMPREHENSIVE INCOME, net of tax	900	1,108
Balances	4,160	3,260	2,152
Interest Rate Swap
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances	(1,198)	(416)
Other comprehensive income (loss) before reclassifications	1,507	(782)
OTHER COMPREHENSIVE INCOME, net of tax	1,507	(782)
Balances	309	(1,198)	(416)
Foreign Currency Translation
Changes in accumulated other comprehensive income (loss), net of tax, by component
Balances	(872)	(1,533)
Other comprehensive income (loss) before reclassifications	102	661
OTHER COMPREHENSIVE INCOME, net of tax	102	661
Balances	$ (770)	$ (872)	$ (1,533)