Comprehensive Income and Accumulated Other Comprehensive Income - Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Unrealized gain (loss) on available-for-sale securities, Pre-tax Amount	$ (4,908)	$ (2,572)	$ 10,133
Change in unrealized losses on available-for-sale securities with OTTI, Pre-Tax Amount		176
Less amortization of differences between fair value and amortized cost for fixed maturity security transfer, Pre-tax Amount	(63)	(40)	(44)
Less reclassification adjustment for gains realized in net income, Pre-Tax Amount	234	2,093	842
Net unrealized gain loss, Pre-Tax Amount	(4,737)	(343)	10,931
Other comprehensive income, Pre-Tax Amount	(4,737)	(343)	10,931
Unrealized gain loss on available-for-sale securities, Tax Expense	(1,718)	(900)	3,546
Change in unrealized losses on available-for-sale securities with OTTI, Tax Expense		62
Less amortization of differences between fair value and amortized cost for fixed maturity security transfer, Tax Expense	(22)	(14)	(15)
Less reclassification adjustment for gains realized in net income, Tax Expense	82	732	295
Net unrealized gain loss, Tax Expense	(1,658)	(120)	3,826
Other comprehensive income, Tax Expense	(1,658)	(120)	3,826
Unrealized gain (loss) on available-for-sale securities, Net-of-Tax Amount	(3,190)	(1,672)	6,587
Change in unrealized losses on available-for-sale securities with OTTI, Net-of-Tax Amount		114
Less amortization of differences between fair value and amortized cost for fixed maturity security transfer, Net-of-Tax Amount	(41)	(26)	(29)
Reclassification adjustment for gains realized in net income, Net-of-Tax Amount	152	1,361	547
Net unrealized gain loss, Net-of-Tax Amount	(3,079)	(223)	7,105
Other comprehensive income, Net-of-Tax Amount	$ (3,079)	$ (223)	$ 7,105