Accumulated Other Comprehensive Income (Loss) (Reclassifications Out of Accumulated Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pretax total	$ (6,464)	$ 7,907	$ (23,019)	$ 2,618
Income taxes	39,637	35,015	108,831	74,186
Amortization of net actuarial loss	7,613	2,372	24,596	17,186
Amortization of prior service credit	(1,041)	(1,038)	(3,122)	(3,115)
Unrealized Gains (Losses) on Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pretax total	108	9,241	(1,545)	16,689
Pension Benefit Adjustment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pretax total	(6,572)	(1,334)	(21,474)	(14,071)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) | Unrealized Gains (Losses) on Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on sales of securities	108	9,241	(1,545)	17,722
Net other-than-temporary impairment losses				(1,033)
Pretax total	108	9,241	(1,545)	16,689
Income taxes	(33)	(3,641)	492	(6,383)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) | Pension Benefit Adjustment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pretax total	(6,572)	(1,334)	(21,474)	(14,071)
Income taxes	2,514	427	8,214	5,381
Amortization of net actuarial loss	(7,613)	(2,372)	(24,596)	(17,186)	[1]
Amortization of prior service credit	$ 1,041	$ 1,038	$ 3,122	$ 3,115	[1]

[1] These components of AOCI are included in the computation of net periodic cost. See Note 9 Employee Benefit Plans for additional details.