Investments - Additional Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) Securities	Dec. 31, 2017 USD ($) Securities
Schedule of Available-for-sale Securities [Line Items]
Document Period End Date	Sep. 30, 2018
Available-for-sale Securities	$ 21,883	$ 30,848
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	$ 4,732	$ 16,899
Number of securities in unrealized loss position | Securities	23	27
Proceeds from sale of investment in fixed maturity securities	$ 17,000
Proceeds from Sale of Other Investments	$ 17,600
Investment security maturity date, start	Jan. 01, 2018
Investment security maturity date, End	Sep. 30, 2018
Gross realized gains and losses of securities	insignificant
Investments on deposit with the state insurance department	$ 4,000
U.S. Treasury securities, obligations of U.S. Government agencies and Municipalities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	21,263	$ 29,764
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	$ 620	$ 1,084