COMPREHENSIVE INCOME (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Before Tax Amount [Abstract]
Other comprehensive loss, before tax	$ (7,253)		$ (3,588)
Tax (Expense) Benefit [Abstract]
Other comprehensive loss, tax (expense) benefit	2,779		1,713
Net of Tax Amount [Abstract]
Other comprehensive loss, net of tax	(4,474)		(1,875)
Net income	20,805		22,866
Comprehensive income	16,331		20,991
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Before Tax Amount [Abstract]
Other comprehensive loss before reclassifications, before tax	(8,571)		(4,706)
Tax (Expense) Benefit [Abstract]
Unrealized losses arising during holding period, tax (expense) benefit	3,283		1,799
Net of Tax Amount [Abstract]
Other Comprehensive Loss Before Reclassification Adjustments, Net Of Tax	(5,288)		(2,907)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Amounts reclassified from accumulated other comprehensive income [Member]
Before Tax Amount [Abstract]
Amounts reclassified from accumulated OCI, before tax	(19)	[1]	(74)	[1]
Tax (Expense) Benefit [Abstract]
Reclassification adjustment for net gains realized in net income, tax (expense) benefit	7	[1]	28	[1]
Net of Tax Amount [Abstract]
Amounts reclassified from accumulated OCI, net of tax	(12)	[1]	(46)	[1]
Accumulated Defined Benefit Plans Adjustment [Member]
Before Tax Amount [Abstract]
Other comprehensive loss before reclassifications, before tax	1,337	[2]	1,192	[2]
Tax (Expense) Benefit [Abstract]
Recognized employee benefit plan net periodic benefit cost, tax (expense) benefit	(511)	[2]	(114)	[2]
Net of Tax Amount [Abstract]
Other Comprehensive Loss Before Reclassification Adjustments, Net Of Tax	$ 826	[2]	$ 1,078	[2]

[1] Reclassification adjustments for net gains on available-for-sale securities are reported as security gains, net on the consolidated statement 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 Footnote 9 - Pension Benefits.