Securities - Summary of Amortized Cost and Estimated Fair Values of Debt Securities Held for Investment (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 1,997	$ 1,428
Gross Unrealized Gains	7	5
Gross Unrealized Losses	(1)
Estimated Fair Value	2,003	1,433
Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	112	133
Gross Unrealized Gains	6	5
Estimated Fair Value	118	138
States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,385	795
Gross Unrealized Gains	1
Gross Unrealized Losses	(1)
Estimated Fair Value	1,385	795
Other Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	500	500
Estimated Fair Value	$ 500	$ 500