Investment Securities - Contractual Maturities of Investments Securities Available for Sale (Detail) $ in Thousands	Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Due in one year, Amortized Cost	$ 501,717
Due after one year through five years, Amortized Cost	89,821
Due after five years through ten years, Amortized Cost	120,691
Due after ten years, Amortized Cost	81,922
Total investment securities available for sale, Amortized Cost	1,516,937
Due in one year, Fair Value	501,565
Due after one year through five years, Fair Value	89,834
Due after five years through ten years, Fair Value	118,331
Due after ten years, Fair Value	80,628
Total investment securities available for sale, Fair Value	1,506,861
Residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	701,764
Securities without a single maturity date, Fair Value	696,428
Equity securities [Member]
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	$ 20,075