CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other comprehensive income, before tax:
Change in accumulated unrealized gain or loss for pension and other post retirement obligations	$ (4,755)	$ (17,213)	$ 9
Change in unrealized losses on derivative instruments used in cash flow hedging relationships	0	3,232	1,861
Unrealized gains (losses) on securities:
Unrealized holding gains (losses) arising during period	46,235	75,609	(2,803)
Reclassification adjustment for (gains) losses, net included in net income	(291)	(30)	0
Other comprehensive gain (loss), before tax	41,189	61,598	(933)
Income tax (expense) benefit related to other comprehensive loss	(16,020)	(23,093)	377
Other comprehensive gain (loss) income, net of tax	25,169	38,505	(556)
Net income	77,068	73,142	63,320
Comprehensive income	102,237	111,647	62,764
Tax Effect Allocated To Each Component Of Comprehensive Income:
Tax effect of unrealized gain (loss) for pension and other postretirement obligations	1,844	6,631	(2)
Tax effect of unrealized losses on derivative instruments used in cash flow hedging relationships	0	(1,252)	(716)
Tax effect of unrealized gains and losses on available-for-sale securities arising during period	(17,977)	(28,484)	1,095
Reclassification adjustment for gains included in net income	113	12	0
Tax effect of unrealized gains on available-for-sale securities arising during period	(17,864)	(28,472)	1,095
Income tax (expense) benefit related to other comprehensive loss	(16,020)	(23,093)	377
Accumulated Other Comprehensive Income By Component: [Abstract]
Unrealized loss for pension and other postretirement obligations	(45,232)	(40,477)	(23,264)
Tax effect	17,447	15,603	8,972
Net unrealized loss for pension and other postretirement obligations	(27,785)	(24,874)	(14,292)
Unrealized losses on derivative instruments used in cash flow hedging relationships	0	0	(3,232)
Tax effect	0	0	1,252
Net unrealized losses on derivative instruments used in cash flow hedging relationships	0	0	(1,980)
Unrealized gain on available-for-sale securities	131,456	85,512	9,933
Tax effect	(49,337)	(31,473)	(3,001)
Net unrealized gain on available-for-sale securities	82,119	54,039	6,932
Accumulated other comprehensive income (loss)	$ 54,334	$ 29,165	$ (9,340)