CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Change in accumulated unrealized gain or loss for pension and other postretirement obligations	$ (17,213)	$ 9	$ 12,434
Change in unrealized losses on derivative instruments used in cash flow hedging relationships	3,232	1,861	1,628
Unrealized gains (losses) on securities:
Unrealized holding (losses) gains arising during period	75,609	(2,803)	(7,286)
Reclassification adjustment for gains included in net income	(30)	0	(7)
Other comprehensive gain (loss), before tax	61,598	(933)	6,769
Income tax (expense) benefit related to other comprehensive loss	(23,093)	377	(2,689)
Other comprehensive gain (loss) income, net of tax	38,505	(556)	4,080
Net income	73,142	63,320	41,445
Comprehensive income	111,647	62,764	45,525
Tax Effect Allocated To Each Component Of Comprehensive Income:
Tax effect of unrealized gain (loss) for pension and other postretirement obligations	6,631	(2)	(4,783)
Tax effect of unrealized losses on derivative instruments used in cash flow hedging relationships	(1,252)	(716)	(626)
Tax effect of unrealized gains and losses on available-for-sale securities arising during period	(28,484)	1,095	2,717
Reclassification adjustment for gains included in net income	12	0	3
Tax effect of unrealized gains on available-for-sale securities arising during period	(28,472)	1,095	2,720
Income tax (expense) benefit related to other comprehensive loss	(23,093)	377	(2,689)
Accumulated Other Comprehensive Income By Component:
Unrealized loss for pension and other postretirement obligations	(40,477)	(23,264)	(23,273)
Tax effect	15,603	8,972	8,974
Net unrealized loss for pension and other postretirement obligations	(24,874)	(14,292)	(14,299)
Unrealized losses on derivative instruments used in cash flow hedging relationships	0	(3,232)	(5,093)
Tax effect	0	1,252	1,968
Net unrealized losses on derivative instruments used in cash flow hedging relationships	0	(1,980)	(3,125)
Unrealized gain on available-for-sale securiies	85,512	9,933	12,736
Tax effect	(31,473)	(3,001)	(4,096)
Net unrealized gain on available-for-sale securities	54,039	6,932	8,640
Accumulated other comprehensive income (loss)	$ 29,165	$ (9,340)	$ (8,784)