Investment Securities - Additional Information on Securities in a Continuous Loss Position (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) Security	Dec. 31, 2015 USD ($) Security
Schedule of Available-for-sale Securities
Number of securities | Security	53	43
Amortized cost basis	$ 209,628	$ 241,561
Unrealized loss	$ 2,113	$ 5,996
Issued by Fannie Mae, Freddie Mac, or Ginnie Mae
Schedule of Available-for-sale Securities
Number of securities | Security	51	40
Amortized cost basis	$ 206,880	$ 236,800
Unrealized loss	$ 2,090	$ 5,895
Issued by Political Subdivisions
Schedule of Available-for-sale Securities
Number of securities | Security	1	2
Amortized cost basis	$ 2,240	$ 4,253
Unrealized loss	$ 21	$ 92
Others
Schedule of Available-for-sale Securities
Number of securities | Security	1	1
Amortized cost basis	$ 508	$ 508
Unrealized loss	$ 2	$ 9