Statement of Other Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Income	$ 159,845	$ 145,573	$ 128,332
Unrealized gain on securities	1,569	8,768	3,994
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax	(1,967)	(2,964)	(455)
Non-credit related unrealized gain (loss) on other-than-temporarily impaired debt securities	(1,330)	(240)	166
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	136	136	136
Unrecognized pension and postretirement (cost) income	(4,207)	(10,672)	1,454
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Pension Cost, Net of Tax	859	(48)	74
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(2,280)	(4,540)	5,037
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 157,565	$ 141,033	$ 133,369