Securities - Contractual Maturity of Investment Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Less than one year, Amortized Cost	$ 46,636
Due after one year through five years, Amortized Cost	72,891
Due after five years through ten years, Amortized Cost	596
Due after ten years, Amortized Cost	55,000
Total Amortized Cost	175,123
Less than one year, Estimated Fair Value	46,678
Due after one year through five years, Estimated Fair Value	72,815
Due after five years through ten years, Estimated Fair Value	598
Due after ten years, Estimated Fair Value	45,250
Total Estimated Fair Value	$ 165,341