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, 2013	Dec. 31, 2012
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	$ 89,238	$ 71,271
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	1,827	853
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value	14,885	3,574
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	204	42
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	104,123	74,845
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	2,031	895
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	42,102	36,480
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	558	129
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	42,102	36,480
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	558	129
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	8,664	17,344
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	9	401
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value	14,885	3,574
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	204	42
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	23,549	20,918
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	213	443
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	38,472	12,453
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	1,260	250
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value	38,472	12,453
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss	1,260	250
Corporate bonds and other [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		4,994
Available-for-sale and held-to-maturity securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss		73
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Fair Value
Available-for-sale and held-to-maturity securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Fair Value		4,994
Available-for-sale and held-to-maturity securities, continuous unrealized loss position, Unrealized Loss		$ 73