Investment Securities - Fair Value of Investment Securities Available for Sale by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Available for Sale, Amortized Cost
Within 1 Year	$ 3
After 1 Year through 5 Years	3,254
After 5 Years through 10 Years	9,736
Over Ten Years	332,349
Total	345,342
Available for Sale, Fair Value
Within 1 Year	3
After 1 Year through 5 Years	3,263
After 5 Years through 10 Years	9,675
Over Ten Years	328,582
Total	341,523
Held to Maturity, Amortized Cost
Within 1 Year	0
After 1 Year through 5 Years	0
After 5 Years through 10 Years	15,492
Over Ten Years	0
Total	15,492
Held to Maturity, Fair Value
Within 1 Year	0
After 1 Year through 5 Years	0
After 5 Years through 10 Years	15,422
Over Ten Years	0
Total	$ 15,422	$ 0