Investment Securities - Contractual Maturities of Investment Securities Available for Sale (Detail) $ in Thousands	Jun. 30, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Due in one year, Amortized Cost	$ 500
Due after one year through five years, Amortized Cost	64,469
Due after five years through ten years, Amortized Cost	78,693
Due after ten years, Amortized Cost	61,099
Total investment securities available for sale, Amortized Cost	817,125
Due in one year, Fair Value	500
Due after one year through five years, Fair Value	65,586
Due after five years through ten years, Fair Value	76,336
Due after ten years, Fair Value	58,892
Total investment securities available for sale, Fair Value	807,574
Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	591,342
Securities without a single maturity date, Fair Value	585,791
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	21,022
Securities without a single maturity date, Fair Value	$ 20,469