Investment Securities - Summary of Investment Securities by Stated Maturity (Detail) $ in Thousands	Dec. 31, 2015 USD ($)
Investments, Debt and Equity Securities [Abstract]
Amortized cost, due in one year or less	$ 0
Amortized cost, due after one year through five years	0
Amortized cost, due after five years through ten years	32,925
Amortized cost, due after ten years	7,000
Mortgage-backed securities, amortized cost	506,111
Amortized cost	546,036
Fair value, due in one year or less	0
Fair value, due after one year through five years	0
Fair value, due after five years through ten years	33,112
Fair value, due after ten years	6,955
Mortgage-backed securities, fair value	500,974
Total debt securities, fair value	$ 541,041