Summary of Significant Accounting Policies - Components of Other Comprehensive Income (Loss) and Related Tax Effects (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Comprehensive Income Available For Sale Securities Adjustment Net Of Tax Period Increase Decrease [Abstract]
Net unrealized gain (loss) on available-for-sale securities	$ 6,091	$ 5,179	$ (1,058)
Reclassification adjustment for (gain) loss on sale of available-for-sale securities	(270)	26	9
Net unrealized gain (loss) on available-for-sale securities	5,821	5,205	(1,049)
Tax expense (benefit)	1,222	1,093	(220)
Other comprehensive income (loss)	$ 4,599	$ 4,112	$ (829)

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Amount before tax, after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities, attributable to parent entity. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount of tax expense (benefit), after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities, attributable to parent entity. Excludes amounts related to other than temporary impairment (OTTI) loss.

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