Comprehensive Income and Accumulated Other Comprehensive Income - Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Unrealized gain (loss) on available-for-sale securities, Pre-Tax Amount	$ 15,670	$ (5,760)	$ 6,960
Reclassification adjustment for gains (losses) realized in net income, Pre-Tax Amount	841	390	(1,106)
Net unrealized gain loss, Pre-Tax Amount	16,511	(5,370)	5,854
Other comprehensive income (loss), Pre-Tax Amount	16,511	(5,370)	5,854
Unrealized gain loss on available-for-sale securities, Tax Expense (Benefit)	3,291	(1,209)	2,137
Reclassification adjustment for gains (losses) realized in net income, Tax Expense (Benefit)	177	82	(387)
Net unrealized gain loss, Tax Expense (Benefit)	3,468	(1,127)	1,750
Other comprehensive income (loss), Tax Expense (Benefit)	3,468	(1,127)	1,750
Unrealized gain (loss) on available-for-sale securities, Net-of-Tax Amount	12,379	(4,551)	4,823
Reclassification adjustment for gains (losses) realized in net income, Net-of-Tax Amount	664	308	(719)
Net unrealized gain loss, Net-of-Tax Amount	13,043	(4,243)	4,104
Other comprehensive income (loss), Net-of-Tax Amount	$ 13,043	$ (4,243)	$ 4,104