Investments - Fair Value and Gross Unrealized Losses of Investments, Available-for-Sale, by the Length of Time (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	$ 32,976	$ 86,000
Less than 12 months, Gross Unrealized Losses	(324)	(3,079)
12 months or longer, Fair value	56,502
12 months or longer, Gross Unrealized Losses	(2,119)
Total Gross Unrealized Losses	(2,443)	(3,079)
Total Fixed Maturities, Available-for-Sale
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	32,976	84,585
Less than 12 months, Gross Unrealized Losses	(324)	(2,968)
12 months or longer, Fair value	55,091
12 months or longer, Gross Unrealized Losses	(2,005)
Total Gross Unrealized Losses	(2,329)	(2,968)
U.S. Government and Agencies
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	7,746	14,837
Less than 12 months, Gross Unrealized Losses	(72)	(303)
12 months or longer, Fair value	10,020
12 months or longer, Gross Unrealized Losses	(293)
Total Gross Unrealized Losses	(365)	(303)
Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	4,083	4,166
Less than 12 months, Gross Unrealized Losses	(28)	(68)
Total Gross Unrealized Losses	(28)	(68)
Revenue and Assessment
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	1,067	2,783
Less than 12 months, Gross Unrealized Losses	(5)	(41)
Total Gross Unrealized Losses	(5)	(41)
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	10,730	41,057
Less than 12 months, Gross Unrealized Losses	(123)	(1,805)
12 months or longer, Fair value	25,235
12 months or longer, Gross Unrealized Losses	(1,022)
Total Gross Unrealized Losses	(1,145)	(1,805)
Agency Backed
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	9,085	21,637
Less than 12 months, Gross Unrealized Losses	(95)	(744)
12 months or longer, Fair value	19,730
12 months or longer, Gross Unrealized Losses	(685)
Total Gross Unrealized Losses	(780)	(744)
Non-Agency Backed - Residential
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	265	105
Less than 12 months, Gross Unrealized Losses	(1)	(7)
12 months or longer, Fair value	106
12 months or longer, Gross Unrealized Losses	(5)
Total Gross Unrealized Losses	(6)	(7)
Preferred stock, available-for-sale
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value		1,415
Less than 12 months, Gross Unrealized Losses		(111)
12 months or longer, Fair value	1,411
12 months or longer, Gross Unrealized Losses	(114)
Total Gross Unrealized Losses	$ (114)	$ (111)