Investment Securities - Additional Information on Securities in a Continuous Loss Position (Detail) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) Security	Dec. 31, 2016 USD ($) Security
Schedule of Available-for-sale Securities
Number of debt securities with unrealized losses | Security	386	397
Debt securities with unrealized losses (percentage of amortized cost)	1.23%	1.79%
Number of securities | Security	45	31
Amortized cost basis	$ 185,358	$ 116,886
Unrealized loss	$ 3,936	$ 3,164
Fannie Mae, Freddie Mac, or Ginnie Mae
Schedule of Available-for-sale Securities
Number of securities | Security	43	28
Amortized cost basis	$ 183,926	$ 112,983
Unrealized loss	$ 3,920	$ 3,111
Other
Schedule of Available-for-sale Securities
Number of securities | Security	2	3
Amortized cost basis	$ 1,432	$ 3,903
Unrealized loss	$ 16	$ 53