River Financial Corporation (Parent Company Only) Financial Information - Statements of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Condensed Income Statements Captions [Line Items]
Other income	$ 275	$ 211
Total interest income	36,685	32,170
Interest expense - note payable	485	249
Legal and other professional services	798	505
Data processing expense	3,527	1,689
Other operating expense	3,731	3,392
Applicable income tax benefit	2,383	4,519
Net income	8,506	8,295
River Financial Corporation
Condensed Income Statements Captions [Line Items]
Cash dividends from River Bank & Trust	3,750	2,250
Other income	22
Total interest income	3,772	2,250
Interest expense - note payable	485	249
Legal and other professional services	394	101
Data processing expense	77	4
Stockholders' meeting expense	12	11
Other operating expense	61	10
Total expenses	1,029	375
Net income before tax benefit	2,743	1,875
Applicable income tax benefit	(182)	(134)
Net income before undistributed net income of River Bank & Trust	2,925	2,009
Equity in undistributed net income of River Bank & Trust	5,581	6,286
Net income	$ 8,506	$ 8,295