Comprehensive Income and Accumulated Other Comprehensive Income - Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Unrealized gain (loss) on available-for-sale securities, Pre-Tax Amount	$ (5,760)	$ 6,960	$ (4,908)
Less amortization of differences between fair value and amortized cost for fixed maturity security transfer, Pre-Tax Amount			(63)
Reclassification adjustment for gains (losses) realized in net income, Pre-Tax Amount	390	(1,106)	234
Net unrealized gain loss, Pre-Tax Amount	(5,370)	5,854	(4,737)
Other comprehensive income (loss), Pre-Tax Amount	(5,370)	5,854	(4,737)
Unrealized gain loss on available-for-sale securities, Tax Expense (Benefit)	(1,209)	2,137	(1,718)
Less amortization of differences between fair value and amortized cost for fixed maturity security transfer, Tax Expense (Benefit)			(22)
Reclassification adjustment for gains (losses) realized in net income, Tax Expense (Benefit)	82	(387)	82
Net unrealized gain loss, Tax Expense (Benefit)	(1,127)	1,750	(1,658)
Other comprehensive income (loss), Tax Expense (Benefit)	(1,127)	1,750	(1,658)
Unrealized gain (loss) on available-for-sale securities, Net-of-Tax Amount	(4,551)	4,823	(3,190)
Less amortization of differences between fair value and amortized cost for fixed maturity security transfer, Net-of-Tax Amount			(41)
Reclassification adjustment for gains (losses) realized in net income, Net-of-Tax Amount	308	(719)	152
Net unrealized gain loss, Net-of-Tax Amount	(4,243)	4,104	(3,079)
Other comprehensive income (loss), Net-of-Tax Amount	$ (4,243)	$ 4,104	$ (3,079)