STOCKHOLDERS' EQUITY - AOCI (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income
Total after-tax amount	$ 1,063,212	$ 983,172	$ 929,067	$ 898,134	$ 851,909	$ 828,593
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income
Total pre-tax amount	6,707		4,977
Total after-tax amount	4,974	$ 5,323	3,699	2,672	$ 1,994	1,190
Unrecognized Net Periodic Benefit Credit
Accumulated Other Comprehensive Income
Total pre-tax amount	5,224		5,602
Total after-tax amount	3,879		4,160	3,060		3,260
Interest Rate Swap
Accumulated Other Comprehensive Income
Total pre-tax amount	2,859		419
Total after-tax amount	2,111		309	(457)		(1,198)
Foreign Currency Translation
Accumulated Other Comprehensive Income
Total pre-tax amount	(1,376)		(1,044)
Total after-tax amount	$ (1,016)		$ (770)	$ 69		$ (872)