STOCKHOLDERS' EQUITY - AOCI components (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Changes in accumulated other comprehensive income, net of tax, by component
Balances	$ 983,172	$ 929,067	$ 851,909	$ 828,593	$ 929,067	$ 828,593
OTHER COMPREHENSIVE INCOME (LOSS), net of tax	(349)	1,624	678	804	1,275	1,482
Balances	1,063,212	983,172	898,134	851,909	1,063,212	898,134
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income, net of tax, by component
Balances	5,323	3,699	1,994	1,190	3,699	1,190
Other comprehensive income (loss) before reclassifications					1,556	1,682
Amounts reclassified from accumulated other comprehensive income					(281)	(200)
OTHER COMPREHENSIVE INCOME (LOSS), net of tax	(349)	1,624	678	804	1,275	1,482
Balances	4,974	5,323	2,672	1,994	4,974	2,672
Unrecognized Net Periodic Benefit Credit
Changes in accumulated other comprehensive income, net of tax, by component
Balances		4,160		3,260	4,160	3,260
Amounts reclassified from accumulated other comprehensive income					(281)	(200)
OTHER COMPREHENSIVE INCOME (LOSS), net of tax					(281)	(200)
Balances	3,879		3,060		3,879	3,060
Interest Rate Swap
Changes in accumulated other comprehensive income, net of tax, by component
Balances		309		(1,198)	309	(1,198)
Other comprehensive income (loss) before reclassifications					1,802	741
OTHER COMPREHENSIVE INCOME (LOSS), net of tax					1,802	741
Balances	2,111		(457)		2,111	(457)
Foreign Currency Translation
Changes in accumulated other comprehensive income, net of tax, by component
Balances		$ (770)		$ (872)	(770)	(872)
Other comprehensive income (loss) before reclassifications					(246)	941
OTHER COMPREHENSIVE INCOME (LOSS), net of tax					(246)	941
Balances	$ (1,016)		$ 69		$ (1,016)	$ 69