Investment Securities - Schedule of Investments in Accordance with Fair Value Measurement (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	$ 10,422	$ 76,831
Total investments fair value	42,429	81,379
Money Market Funds [Member]
Class of securities:
Money market funds	32,007	4,548
Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	8,647	60,567
Total investments fair value	40,654	65,115
Level 1 | Money Market Funds [Member]
Class of securities:
Money market funds	32,007	4,548
Level 2
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	1,775	16,264
Total investments fair value	1,775	16,264
U.S. Government Treasury Securities [Member]
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	250	249
U.S. Government Treasury Securities [Member] | Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	250	249
Obligations of U.S. Government Sponsored Enterprises [Member]
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	2,742	59,371
Obligations of U.S. Government Sponsored Enterprises [Member] | Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	1,497	47,489
Obligations of U.S. Government Sponsored Enterprises [Member] | Level 2
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	1,245	11,882
Corporate Debt Securities [Member]
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	3,681	11,415
Corporate Debt Securities [Member] | Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	3,151	7,033
Corporate Debt Securities [Member] | Level 2
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	530	4,382
Foreign Corporate Debt Securities [Member]
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	3,749	5,796
Foreign Corporate Debt Securities [Member] | Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	$ 3,749	$ 5,796