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