CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Other comprehensive income, before tax:
Change in accumulated unrealized gain or loss for pension and other post retirement obligations	$ 682	$ 174
Change in unrealized losses on derivative instruments used in cash flow hedging relationships	0	788
Unrealized holding (losses) gains arising during period	(7,010)	8,977
Other comprehensive gain (loss), before tax:	(6,328)	9,939
Income tax (expense) benefit related to other comprehensive income	2,160	(3,821)
Other comprehensive gain (loss), net of tax:	(4,168)	6,118
Net income	18,826	16,160
Comprehensive income	14,658	22,278
Tax Effect Allocated To Each Component Of Comprehensive Income:
Tax effect of unrealized gain (loss) for pension and other postretirement obligations	(264)	(68)
Tax effect of unrealized losses on derivative instruments used in cash flow hedging relationships	0	(303)
Tax effect of unrealized gains and losses on available-for-sale securities arising during period	2,424	(3,450)
Income tax (expense) benefit related to other comprehensive loss	2,160	(3,821)
Accumulated Other Comprehensive Income By Component: [Abstract]
Unrealized loss for pension and other postretirement obligations	(39,795)	(23,090)
Tax effect	15,339	8,904
Net unrealized loss for pension and other postretirement obligations	(24,456)	(14,186)
Unrealized losses on derivative instruments used in cash flow hedging relationships	0	(2,445)
Tax effect	0	949
Net unrealized losses on derivative instruments used in cash flow hedging relationships	0	(1,496)
Unrealized gain on available-for-sale securities	78,503	18,910
Tax effect	(29,050)	(6,451)
Net unrealized gain on available-for-sale securities	49,453	12,459
Accumulated other comprehensive income (loss)	$ 24,997	$ (3,223)