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	Mar. 31, 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	$ 546,693	$ 653,523
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	11,399	22,213
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value	38,681	9,777
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	1,665	645
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	585,374	663,300
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	13,064	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	187,995	316,394
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	4,424	10,973
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value	17,998	4,153
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	859	346
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	205,993	320,547
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	5,283	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	258,426	228,423
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	4,821	7,623
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value	10,643	5,624
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	356	299
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	269,069	234,047
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	5,177	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	100,272	108,706
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	2,154	3,617
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value	10,040
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	450
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	110,312	108,706
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	$ 2,604	$ 3,617