Investment Securities - Contractual Maturities of Investment Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Due in one year, Amortized Cost	$ 115
Due after one year through five years, Amortized Cost	69,007
Due after five years through ten years, Amortized Cost	84,257
Due after ten years, Amortized Cost	129,833
Total investment securities available for sale, Amortized Cost	771,375
Due in one year, Fair Value	115
Due after one year through five years, Fair Value	70,015
Due after five years through ten years, Fair Value	80,698
Due after ten years, Fair Value	123,956
Total investment securities available for sale, Fair Value	758,421
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	465,092
Securities without a single maturity date, Fair Value	459,577
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	23,071
Securities without a single maturity date, Fair Value	$ 24,060