Securities Available-for-Sale - Maturity Distribution of Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 186,348
After one but within five years, Amortized Cost	203,010
After five but within ten years, Amortized Cost	130,087
More than ten years, Amortized Cost	5,701
Non-maturing, Amortized Cost	1,616
Amortized Cost	526,762	$ 404,977
Within one year, Fair Value	186,336
After one but within five years, Fair Value	202,873
After five but within ten years, Fair Value	129,948
More than ten years, Fair Value	5,313
Non-maturing, Fair Value	1,662
Total, Fair Value	$ 526,132	$ 404,623