STOCKHOLDERS' EQUITY - AOCI (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income
Total after-tax amount	$ 983,172	$ 929,067	$ 851,909	$ 828,593
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income
Total pre-tax amount	7,178	4,977
Total after-tax amount	5,323	3,699	1,994	1,190
Unrecognized Net Periodic Benefit Credit
Accumulated Other Comprehensive Income
Total pre-tax amount	5,413	5,602
Total after-tax amount	4,019	4,160	3,160	3,260
Interest Rate Swap
Accumulated Other Comprehensive Income
Total pre-tax amount	2,394	419
Total after-tax amount	1,767	309	(623)	(1,198)
Foreign Currency Translation
Accumulated Other Comprehensive Income
Total pre-tax amount	(629)	(1,044)
Total after-tax amount	$ (463)	$ (770)	$ (543)	$ (872)