Supplemental Information about Changes to Accumulated Other Comprehensive Income - Summary of Reclassification out of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Comprehensive Income Loss Reclassification Adjustments [Line Items]
Amortization of Prior service cost	$ 2,276	$ 2,146	$ 2,080
Amortization of actuarial (gain) loss	16,090	12,653	10,071
Total amortization	18,366	14,799	12,146
Tax	(234,654)	(236,669)	(226,166)
Tax	(24,732)	16,894	4,887
Reclassification out of Accumulated Other Comprehensive Income [Member]
Other Comprehensive Income Loss Reclassification Adjustments [Line Items]
Total after tax	2,624
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized gains (losses) on available for sale assets [Member]
Other Comprehensive Income Loss Reclassification Adjustments [Line Items]
Realized (gains) losses	(9,606)
Amortization of (discount) premium	(6,569)
Total before tax	(16,175)
Tax	6,861
Total after tax	(9,314)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension adjustments [Member]
Other Comprehensive Income Loss Reclassification Adjustments [Line Items]
Amortization of Prior service cost	2,276
Amortization of actuarial (gain) loss	16,090
Total amortization	18,366
Tax	(6,428)
Total after tax	$ 11,938