Interest-bearing Time Deposits in Banks and Securities - Continuous Unrealized-Loss Position of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule Of Available For Sale And Held To Maturity Securities Continuous Unrealized Loss Position [Line Items]
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Fair Value	$ 272,171	$ 653,523
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	6,652	22,213
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value	135,369	9,777
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	2,783	645
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	407,540	663,300
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	9,435	22,858
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale And Held To Maturity Securities Continuous Unrealized Loss Position [Line Items]
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Fair Value	41,095	316,394
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	160	10,973
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value	101,800	4,153
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	1,856	346
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	142,895	320,547
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	2,016	11,319
Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities Continuous Unrealized Loss Position [Line Items]
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Fair Value	133,104	228,423
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	4,417	7,623
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value	23,427	5,624
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	594	299
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	156,531	234,047
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	5,011	7,922
Commercial Mortgage-Backed Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities Continuous Unrealized Loss Position [Line Items]
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Fair Value	97,972	108,706
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	2,075	3,617
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value	10,142
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	333
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	108,114	108,706
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	$ 2,408	$ 3,617