COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
COMPREHENSIVE INCOME [Abstract]
Unrealized gains (losses) arising during holding period, Before tax amount	$ (700)	$ 5,956	$ (226)	$ 20,125
Reclassification adjustment for net gains realized in net income, Before tax amount	(23)	(86)	(1,094)	(88)
Recognized employee benefit plan net periodic benefit cost, Before tax amount	1,533	1,511	3,066	3,022
Other comprehensive income (loss), Before tax amount	810	7,381	1,746	23,059
Unrealized gains (losses) arising during holding period, Tax effect	267	(2,279)	84	(7,699)
Reclassification adjustment for net gains realized in net income, Tax effect	8	33	418	34
Recognized employee benefit plan net periodic benefit cost, Tax effect	(586)	(578)	(1,172)	(1,156)
Other comprehensive income (loss), Tax effect	(311)	(2,824)	(670)	(8,821)
Unrealized gains (losses) arising during holding period, Net of tax amount	(433)	3,677	(142)	12,426
Reclassification adjustment for net gains realized in net income, Net of tax amount	(15)	(53)	(676)	(54)
Recognized employee benefit plan net periodic benefit cost, Net of tax amount	947	933	1,894	1,866
Other comprehensive income (loss), net of tax	499	4,557	1,076	14,238
Net income	37,889	34,692	75,982	57,241
Comprehensive income	$ 38,388	$ 39,249	$ 77,058	$ 71,479