COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Before Tax Amount [Abstract]
Other comprehensive loss before reclassifications, before tax				$ 380	$ 22,705
Amounts reclassified from accumulated OCI, before tax				(55)	(1)
Other comprehensive income, before tax		$ (6,897)	$ 11,376	3,919	24,180
Recognized employee benefit plan net periodic benefit cost, before tax (2)				3,594	1,476
Tax Effect [Abstract]
Unrealized losses arising during holding period, tax effect				(168)	(8,697)
Reclassification adjustment for net gains realized in net income, tax effect				21
Recognized employee benefit plan net periodic benefit cost, tax effect				(1,374)	(564)
Other comprehensive income, tax effect		2,642	(4,356)	(1,521)	(9,261)
Net of Tax Amount [Abstract]
Other Comprehensive Loss Before Reclassification Adjustments, Net Of Tax				212	14,008
Amounts reclassified from accumulated OCI, net of tax				(34)	(1)
Pension and other postretirement benefits		1,110	456	2,220	912
Other comprehensive income, net of tax		(4,255)	7,020	2,398	14,919
Net income		39,713	30,868	71,979	59,312
Comprehensive income		35,458	37,888	$ 74,377	$ 74,231
Reclassification Adjustment For Net Losses (Gains) Realized In Net Income [Member]
Before Tax Amount [Abstract]
Amounts reclassified from accumulated OCI, before tax	[1]	(41)	(5)
Tax Effect [Abstract]
Reclassification adjustment for net gains realized in net income, tax effect	[1]	16	2
Net of Tax Amount [Abstract]
Amounts reclassified from accumulated OCI, net of tax	[1]	(25)	(3)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Before Tax Amount [Abstract]
Other comprehensive loss before reclassifications, before tax		(8,653)	10,643
Tax Effect [Abstract]
Unrealized losses arising during holding period, tax effect		3,313	(4,076)
Net of Tax Amount [Abstract]
Other Comprehensive Loss Before Reclassification Adjustments, Net Of Tax		(5,340)	6,567
Accumulated Defined Benefit Plans Adjustment [Member]
Before Tax Amount [Abstract]
Other comprehensive loss before reclassifications, before tax	[2]		738
Recognized employee benefit plan net periodic benefit cost, before tax (2)	[2]	1,797
Tax Effect [Abstract]
Recognized employee benefit plan net periodic benefit cost, tax effect	[2]	(687)	(282)
Net of Tax Amount [Abstract]
Other Comprehensive Loss Before Reclassification Adjustments, Net Of Tax	[2]		$ 456
Pension and other postretirement benefits	[2]	$ (1,110)

[1] Reclassification adjustments for net gains (losses) on available-for-sale securities are reported as net security gains on the consolidated statements of income.

[2] Recognized employee benefit plan net periodic benefit cost include amortization of unrecognized transition amount, recognized prior service cost and recognized net loss. For more information, see Note 9 - Pension Benefits.