Investment Securities - Contractual Maturities of Investments Securities Available for Sale (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Amortized Cost
Due in one year	$ 18,770
Due after one year through five years	73,904
Due after five years through ten years	114,174
Due after ten years	58,543
Total investment securities available for sale	1,315,723
Fair Value
Due in one year	18,654
Due after one year through five years	74,158
Due after five years through ten years	112,063
Due after ten years	56,098
Total investment securities available for sale	1,297,373
Residential mortgage-backed securities
Amortized Cost
Securities without a single maturity date	1,029,827
Fair Value
Securities without a single maturity date	1,015,542
Equity securities
Amortized Cost
Securities without a single maturity date	20,505
Fair Value
Securities without a single maturity date	$ 20,858