Reclassifications Out of Accumulated Other Comprehensive Loss ("AOCL") - Reclassifications of Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain on sales of securities	$ 182	$ 1,019	$ 5,317		$ 17,764
Income before income taxes	189,065	180,161	566,816		557,636
Income tax expense (Benefit)	(68,807)	(65,961)	(212,616)		(202,244)
Net gain on sales of securities, net of tax	(109)	(614)	(3,171)		(3,709)
Income tax expense (Benefit)	(73)	(405)	(2,146)		(2,503)
Total reclassifications for the period			1,601	[1]
Reclassification out of Accumulated Other Comprehensive Income (loss) | Unrealized gains on available for sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain on sales of securities			5,317	[1]
Income tax expense (Benefit)			(2,146)	[1]
Net gain on sales of securities, net of tax			3,171	[1]
Reclassification out of Accumulated Other Comprehensive Income (loss) | Amortization of defined benefit pension
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior-service costs			186	[1],[2]
Actuarial losses			(2,820)	[1],[2]
Income before income taxes			(2,634)	[1]
Income tax expense (Benefit)			1,064	[1]
Amortization of defined benefit pension plan items, net of tax			$ (1,570)	[1]

[1] Amounts in parentheses indicate expense items.

[2] Please see Note 9, “Pension and Other Post-Retirement Benefits,” for additional information.