STOCKHOLDERS' EQUITY - AOCI (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income
Total after-tax amount	$ 929,067	$ 828,593	$ 763,043	$ 717,682
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income
Total pre-tax amount	4,977	1,586	260
Total after-tax amount	3,699	1,190	203	$ (14,238)
Unrecognized Net Periodic Benefit Credit
Accumulated Other Comprehensive Income
Total pre-tax amount	5,602	4,390	2,898
Total after-tax amount	4,160	3,260	2,152
Interest Rate Swap
Accumulated Other Comprehensive Income
Total pre-tax amount	419	(1,622)	(563)
Total after-tax amount	309	(1,198)	(416)
Foreign Currency Translation
Accumulated Other Comprehensive Income
Total pre-tax amount	(1,044)	(1,182)	(2,075)
Total after-tax amount	$ (770)	$ (872)	$ (1,533)