Securities - Debt Securities Available for Sale by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014
Amortized Cost And Fair Value Debt Securities [Abstract]
Due in one year or less, amortized cost	$ 500
Due after one year through five years, amortized cost	0
Due after five years through ten years, amortized cost	209,134
Due after ten years through fifteen years, amortized cost	32,409
Mortgage-backed GSE securities: residential, amortized cost	281,852
Total amortized cost	523,895
Due in one year or less, fair value	500
Due after one year through five years, fair value	0
Due after five years through ten years, fair value	200,791
Due after ten years through fifteen years, fair value	30,348
Mortgage-backed GSE securities: residential, fair value	275,486
Total fair value	$ 507,125