Investment Securities - Additional Information on Securities in a Continuous Loss Position (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($) Security	Dec. 31, 2015 USD ($) Security
Schedule of Available-for-sale Securities
Number of securities | Security	30	43
Amortized cost basis	$ 110,947	$ 241,561
Unrealized loss	$ 1,074	$ 5,996
Issued by Fannie Mae, Freddie Mac, or Ginnie Mae
Schedule of Available-for-sale Securities
Number of securities | Security	27	40
Amortized cost basis	$ 106,982	$ 236,800
Unrealized loss	$ 1,025	$ 5,895
Issued by Political Subdivisions
Schedule of Available-for-sale Securities
Number of securities | Security	0	2
Amortized cost basis	$ 0	$ 4,253
Unrealized loss	$ 0	$ 92
Others
Schedule of Available-for-sale Securities
Number of securities | Security	3	1
Amortized cost basis	$ 3,965	$ 508
Unrealized loss	$ 49	$ 9