Securities Available-for-Sale - Additional Information (Detail)	3 Months Ended	6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Security	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) Security
Schedule of Available-for-sale Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements		$ 1,268,349,000		$ 1,147,207,000
Securities available-for-sale are securities at fair value pledged for borrowing		49,416,000		$ 53,396,000
Proceeds from sales of securities available-for-sale		$ 0	$ 1,946,000
Gross gains on sales of securities	$ 45,000		45,000
Federal Home Loan Bank [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross gains on sales of securities			$ 33,000
Securities AFS [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted average remaining life of investment securities available-for-sale		5 years 4 months 24 days
Number of securities, temporarily impaired for less than 12 months | Security		13		49
Number of securities, temporarily impaired for 12 months or longer | Security		27		15
Number of securities, temporarily impaired, total | Security		269		270
U.S. Government Sponsored Enterprises [Member] | Securities AFS [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted average remaining life		$ 10,000,000
U.S. Government Agency and Sponsored Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements		$ 173,235,000		$ 210,780,000