Securities (Year End Securities with Unrealized Losses Segregated by Length of Impairment) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	$ 2,078,455
Held to Maturity, Less than 12 Months, Unrealized Losses	113,655
Held to Maturity, More than 12 Months, Estimated Fair Value	266,566
Held to Maturity, More than 12 Months, Unrealized Losses	24,349
Held to Maturity, Total Estimated Fair Value	2,345,021
Held to Maturity, Total Unrealized Losses	138,004
Available for Sale, Less than 12 Months, Estimated Fair Value	766,904
Available for Sale, Less than 12 Months, Unrealized Losses	8,693
Available for Sale, More than 12 Months, Estimated Fair Value	2,713
Available for Sale, More than 12 Months, Unrealized Losses	282
Available for Sale, Total Estimated Fair Value	769,617
Available for Sale, Total Unrealized Losses	8,975
States and Political Subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	2,071,521	353,626
Held to Maturity, Less than 12 Months, Unrealized Losses	113,512	4,993
Held to Maturity, More than 12 Months, Estimated Fair Value	266,566	0
Held to Maturity, More than 12 Months, Unrealized Losses	24,349	0
Held to Maturity, Total Estimated Fair Value	2,338,087	353,626
Held to Maturity, Total Unrealized Losses	137,861	4,993
Available for Sale, Less than 12 Months, Estimated Fair Value	679,923
Available for Sale, Less than 12 Months, Unrealized Losses	7,492
Available for Sale, Total Estimated Fair Value	679,923
Available for Sale, Total Unrealized Losses	7,492
US Government Corporations and Agencies Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Available for Sale, Less than 12 Months, Estimated Fair Value	53,980
Available for Sale, Less than 12 Months, Unrealized Losses	44
Available for Sale, Total Estimated Fair Value	53,980
Available for Sale, Total Unrealized Losses	44
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	6,934
Held to Maturity, Less than 12 Months, Unrealized Losses	143
Held to Maturity, Total Estimated Fair Value	6,934
Held to Maturity, Total Unrealized Losses	143
Available for Sale, Less than 12 Months, Estimated Fair Value	33,001	3,007
Available for Sale, Less than 12 Months, Unrealized Losses	1,157	24
Available for Sale, More than 12 Months, Estimated Fair Value	2,713	59
Available for Sale, More than 12 Months, Unrealized Losses	282	1
Available for Sale, Total Estimated Fair Value	35,714	3,066
Available for Sale, Total Unrealized Losses	$ 1,439	$ 25