Indemnification Asset - Summary of Activity in Balance of Indemnification Asset (Liability) (Detail) - USD ($) $ in Thousands		12 Months Ended
	May 09, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
FDIC Indemnification Asset [Roll Forward]
Beginning balance		$ (744)	$ (521)	$ (349)
Effect of actual covered losses (recoveries) and increase (decrease) in estimated future covered losses		(192)	(412)	(93)
Change in estimated "true up" liability		(32)	(86)	(71)
Reimbursable expenses, net			2	4
Payments made (received)	$ (184)	256	273	(12)
Gain on termination of loss share agreement	$ (712)	712
Ending balance			(744)	(521)
Amount of indemnification asset (liability) recorded in other assets			(60)	77
Amount of indemnification liability recorded in other liabilities			(684)	(598)
Ending balance		$ (744)	$ (521)	$ (349)