COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
COMPREHENSIVE INCOME [Abstract]
Unrealized gains (losses) arising during holding period, Before tax amount	$ (2,082)	$ (11,169)	$ (2,308)	$ 8,956
Reclassification adjustment for net gains realized in net income, Before tax amount	(5)	(1)	(1,099)	(89)
Recognized employee benefit plan net periodic benefit cost, Before tax amount	1,533	1,511	4,599	4,533
Other comprehensive income (loss), Before tax amount	(554)	(9,659)	1,192	13,400
Unrealized gains (losses) arising during holding period, Tax effect	796	4,275	880	(3,424)
Reclassification adjustment for net gains realized in net income, Tax effect	2		420	34
Recognized employee benefit plan net periodic benefit cost, Tax effect	(586)	(578)	(1,758)	(1,734)
Other comprehensive income (loss), Tax effect	212	3,697	(458)	(5,124)
Unrealized gains (losses) arising during holding period, Net of tax amount	(1,286)	(6,894)	(1,428)	5,532
Reclassification adjustment for net gains realized in net income, Net of tax amount	(3)	(1)	(679)	(55)
Recognized employee benefit plan net periodic benefit cost, Net of tax amount	947	933	2,841	2,799
Other comprehensive income (loss), net of tax	(342)	(5,962)	734	8,276
Net income	39,528	37,817	115,510	95,058
Comprehensive income	$ 39,186	$ 31,855	$ 116,244	$ 103,334