STOCKHOLDERS' EQUITY - AOCI (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income
Total after-tax amount	$ 1,211,361	$ 1,205,859	$ 1,151,401	$ 1,063,212	$ 983,172	$ 929,067
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income
Total pre-tax amount	8,846		9,566
Total after-tax amount	6,569	$ 6,386	7,103	4,974	$ 5,323	3,699
Unrecognized Net Periodic Benefit Credit
Accumulated Other Comprehensive Income
Total pre-tax amount	8,622		9,287
Total after-tax amount	6,402		6,896	3,879		4,160
Interest Rate Swap
Accumulated Other Comprehensive Income
Total pre-tax amount	2,955		3,526
Total after-tax amount	2,183		2,604	2,111		309
Foreign Currency Translation
Accumulated Other Comprehensive Income
Total pre-tax amount	(2,731)		(3,247)
Total after-tax amount	$ (2,016)		$ (2,397)	$ (1,016)		$ (770)