Securities - Maturity of Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Estimated Fair Value	$ 14,654
Estimated Fair Value, Total	505,913
Amortized cost, Total	14,511
Amortized Cost, Total	499,413
Held for Investment [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Estimated Fair Value, Within one year	5,723
Estimated Fair Value, After one year but within five years	7,605
Estimated Fair Value, After five years but within ten years	886
Estimated Fair Value, After ten years	440
Estimated Fair Value	14,654
Amortized cost, Within one year	5,705
Amortized cost, After one year but within five years	7,547
Amortized cost, After five years but within ten years	867
Amortized cost, After ten years	392
Amortized cost, Total	14,511
Available for Sale [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Estimated Fair Value, Within one year	260,550
Estimated Fair Value, After one year but within five years	115,492
Estimated Fair Value, After five years but within ten years	33,862
Estimated Fair Value, After ten years	86,182
Total debt securities	496,086
Estimated Fair Value, Equity securities	9,827
Estimated Fair Value, Total	505,913
Amortized Cost, Within one year	260,548
Amortized Cost, After one year but within five years	113,656
Amortized Cost, After five years but within ten years	33,120
Amortized Cost, After ten years	84,388
Total debt securities	491,712
Amortized Cost, Equity securities	7,701
Amortized Cost, Total	$ 499,413