Securities Available-for-Sale - Maturity Distribution of Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 217,903
After one but within five years, Amortized Cost	232,419
After five but within ten years, Amortized Cost	105,748
More than ten years, Amortized Cost	5,700
Non-maturing, Amortized Cost	1,616
Amortized Cost	563,386	$ 404,977
Within one year, Fair Value	217,912
After one but within five years, Fair Value	232,311
After five but within ten years, Fair Value	105,767
More than ten years, Fair Value	5,292
Non-maturing, Fair Value	1,651
Total, Fair Value	$ 562,933	$ 404,623