Securities Available-for-Sale - Maturity Distribution of Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 139,707
After one but within five years, Amortized Cost	160,760
After five but within ten years, Amortized Cost	100,082
More than 10 years, Amortized Cost	8,004
Non-maturing, Amortized Cost	1,653
Amortized Cost	410,206	$ 448,210
Within one year, Fair Value	139,698
After one but within five years, Fair Value	161,327
After five but within ten years, Fair Value	100,313
More than 10 years, Fair Value	7,176
Non-maturing, Fair Value	1,700
Total, Fair Value	$ 410,214	$ 448,390