CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Other comprehensive income, before tax:
Change in accumulated unrealized gain or loss for pension and other post retirement obligations	$ 683	$ 174	$ 1,365	$ 349
Change in unrealized losses on derivative instruments used in cash flow hedging relationships	0	804	0	1,592
Unrealized gains on securities:
Unrealized holding gains arising during period	51,396	19,425	44,386	28,402
Reclassification adjustment for gains included in net income	0	(106)	0	(106)
Other comprehensive income, before tax:	52,079	20,297	45,751	30,237
Income tax (expense) benefit related to other comprehensive loss	(19,909)	(7,620)	(17,749)	(11,441)
Other comprehensive income, net of tax:	32,170	12,677	28,002	18,796
Net income	21,071	17,986	39,897	34,146
Comprehensive income	53,241	30,663	67,899	52,942
Tax Effect Allocated To Each Component Of Comprehensive Income:
Tax effect of unrealized loss for pension and other postretirement obligations	(266)	(67)	(530)	(135)
Tax effect of unrealized losses on derivative instruments used in cash flow hedging relationships	0	(310)	0	(613)
Tax effect of unrealized gains and losses on available-for-sale securities arising during period	(19,643)	(7,243)	(17,219)	(10,693)
Income tax (expense) benefit related to other comprehensive loss	(19,909)	(7,620)	(17,749)	(11,441)
Accumulated Other Comprehensive Income By Component: [Abstract]
Unrealized loss for pension and other postretirement obligations	(39,112)		(39,112)		(40,477)
Tax effect	15,073		15,073		15,603
Net unrealized loss for pension and other postretirement obligations	(24,039)		(24,039)		(24,874)
Unrealized losses on derivative instruments used in cash flow hedging relationships	0		0		0
Tax effect	0		0		0
Net unrealized losses on derivative instruments used in cash flow hedging relationships	0		0		0
Unrealized gain on available-for-sale securities	129,898		129,898		85,512
Tax effect	(48,692)		(48,692)		(31,473)
Net unrealized gain on available-for-sale securities	81,206		81,206		54,039
Accumulated other comprehensive income (loss)	$ 57,167		$ 57,167		$ 29,165