Revenue Recognition - Summary of Non Interest Income, Segregated by Revenue Streams in-Scope and Out-of-Scope of Topic 606 (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Noninterest income:
Gain on OREO, net		$ 2	$ 3,540	$ 4
Other	$ 1,824	1,809	4,393	4,839
Total noninterest income	10,112	10,038	32,723	29,536
Service Charges on Deposit Accounts [Member]
Noninterest income:
Revenue from contract with customer	4,295	4,085	12,431	11,794
Trust and Investment Services [Member]
Noninterest income:
Revenue from contract with customer	2,182	2,523	6,738	7,432
Bankcard Services [Member]
Noninterest income:
Revenue from contract with customer	875	927	2,637	2,563
Accounting Standards Update 2014-09 [Member]
Noninterest income:
Gain on OREO, net		2	3,540	4
Other	1,824	1,267	4,393	3,895
Total noninterest income	9,176	8,804	29,739	25,688
Accounting Standards Update 2014-09 [Member] | Service Charges on Deposit Accounts [Member]
Noninterest income:
Revenue from contract with customer	4,295	4,085	12,431	11,794
Accounting Standards Update 2014-09 [Member] | Trust and Investment Services [Member]
Noninterest income:
Revenue from contract with customer	2,182	2,523	6,738	7,432
Accounting Standards Update 2014-09 [Member] | Bankcard Services [Member]
Noninterest income:
Revenue from contract with customer	875	927	2,637	2,563
Accounting Standards Update 2014-09 Not Adopted [Member]
Noninterest income:
Total noninterest income	$ 936	$ 1,234	$ 2,984	$ 3,848