Investment Securities - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) Investment	Dec. 31, 2015 USD ($) Investment	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Carrying value of securities pledged to secure public deposits and for other purposes as required by law	$ 356,700	$ 210,100
Pledging requirements for credit derivatives and SWAP agreements - securities	$ 1,400
Number of investments in non-federal issuer representing more than 10% of shareholders' equity | Investment	0	0
Maximum investment in any single non-federal issuer representing shareholders' equity	10.00%	10.00%
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Other than temporary impairment charges	$ 0	$ 5	$ 0