Investment Securities - Schedule of Investments in Accordance with Fair Value Measurement (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	$ 3,153	$ 3,660
Total investments fair value	31,837	34,440
Money Market Funds [Member]
Class of securities:
Money market funds	28,684	30,780
Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	1,908	2,416
Total investments fair value	30,592	33,196
Level 1 | Money Market Funds [Member]
Class of securities:
Money market funds	28,684	30,780
Level 2
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	1,245	1,244
Total investments fair value	1,245	1,244
Obligations of U.S. Government Sponsored Enterprises [Member]
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	2,242	2,239
Obligations of U.S. Government Sponsored Enterprises [Member] | Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	997	995
Obligations of U.S. Government Sponsored Enterprises [Member] | Level 2
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	1,245	1,244
Corporate Debt Securities [Member]
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	911	1,421
Corporate Debt Securities [Member] | Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	$ 911	$ 1,421