Accumulated Other Comprehensive Income (Loss) (Reclassifications Out of Accumulated Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pretax total	$ (32,878)	$ 3,141		$ (17,853)
Income taxes	143,895	116,345		123,644
Amortization of net actuarial loss	32,645	22,587		32,033
Amortization of prior service credit	(4,163)	(4,153)		(4,385)
Unrealized Gains (Losses) on Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pretax total	(4,396)	21,575		9,795
Pension Benefit Adjustment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pretax total	(28,482)	(18,434)		$ (27,648)
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	(2,147)	23,276
Net other-than-temporary impairment losses	(2,249)	(1,701)
Pretax total	(4,396)	21,575
Income taxes	1,551	(7,959)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) | Pension Benefit Adjustment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pretax total	(28,482)	(18,434)
Income taxes	10,893	7,051
Amortization of net actuarial loss	(32,645)	(22,587)	[1]
Amortization of prior service credit	$ 4,163	$ 4,153	[1]

[1] These components of AOCI are included in the computation of net periodic cost. See Note 13 Employee Benefit Plans for additional details.