Investment Securities - Contractual Maturities of Investment Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Due in one year, Amortized Cost	$ 150
Due after one year through five years, Amortized Cost	56,119
Due after five years through ten years, Amortized Cost	106,520
Due after ten years, Amortized Cost	176,685
Total investment securities available for sale, Amortized Cost	934,704
Due in one year, Fair Value	151
Due after one year through five years, Fair Value	55,262
Due after five years through ten years, Fair Value	103,815
Due after ten years, Fair Value	169,280
Total investment securities available for sale, Fair Value	910,809
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	547,303
Securities without a single maturity date, Fair Value	535,283
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	47,927
Securities without a single maturity date, Fair Value	$ 47,018