STOCKHOLDERS' EQUITY - AOCI components (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Changes in accumulated other comprehensive income, net of tax, by component
Balances	$ 929,067	$ 828,593
OTHER COMPREHENSIVE INCOME, net of tax	1,624	804
Balances	983,172	851,909
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income, net of tax, by component
Balances	3,699	1,190
Other comprehensive income (loss) before reclassifications	1,765	904
Amounts reclassified from accumulated other comprehensive income	(141)	(100)
OTHER COMPREHENSIVE INCOME, net of tax	1,624	804
Balances	5,323	1,994
Unrecognized Net Periodic Benefit Credit
Changes in accumulated other comprehensive income, net of tax, by component
Balances	4,160	3,260
Amounts reclassified from accumulated other comprehensive income	(141)	(100)
OTHER COMPREHENSIVE INCOME, net of tax	(141)	(100)
Balances	4,019	3,160
Interest Rate Swap
Changes in accumulated other comprehensive income, net of tax, by component
Balances	309	(1,198)
Other comprehensive income (loss) before reclassifications	1,458	575
OTHER COMPREHENSIVE INCOME, net of tax	1,458	575
Balances	1,767	(623)
Foreign Currency Translation
Changes in accumulated other comprehensive income, net of tax, by component
Balances	(770)	(872)
Other comprehensive income (loss) before reclassifications	307	329
OTHER COMPREHENSIVE INCOME, net of tax	307	329
Balances	$ (463)	$ (543)