COMPREHENSIVE INCOME (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net unrealized gains on available-for- sale securities, before tax amount [Abstract]
Unrealized gains arising during holding period, before tax amount	$ 6,820	$ 14,563	$ 10,519	$ 56,981
Less: Reclassification adjustment for net gains realized in net income, before tax amount	(39)	(2,047)	(290)	(12,109)
Recognized employee benefit plan net periodic benefit cost, before tax amount	704	947	3,088	2,213
Other comprehensive income	7,485	13,463	13,317	47,085
Net unrealized gains on available-for- sale securities, tax (expense) benefit [Abstract]
Unrealized gains arising during holding period, tax (expense) benefit	(2,613)	(5,578)	(4,034)	(21,823)
Less: Reclassification adjustment for net gains realized in net income, tax (expense) benefit	15	783	111	4,632
Recognized employee benefit plan net periodic benefit cost, tax (expense) benefit	(269)	(362)	(1,181)	(846)
Other comprehensive income	(2,867)	(5,157)	(5,104)	(18,037)
Net unrealized gains on available-for- sale securities, net of tax amount [Abstract]
Unrealized gains arising during holding period, net of tax amount	4,207	8,985	6,485	35,158
Reclassification adjustment for net gains realized in net income, net of tax amount	(24)	(1,264)	(179)	(7,477)
Recognized employee benefit plan net periodic benefit cost, net of tax amount	435	585	1,907	1,367
Other comprehensive income	4,618	8,306	8,213	29,048
Net income	23,825	11,934	67,315	24,266
Comprehensive income	$ 28,443	$ 20,240	$ 75,528	$ 53,314