Investment Securities - Schedule of Investments in Accordance with Fair Value Measurement (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	$ 24,062	$ 76,831
Total investments fair value	67,428	81,379
Money Market Funds [Member]
Class of securities:
Money market funds	43,366	4,548
Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	14,030	60,567
Total investments fair value	57,396	65,115
Level 1 | Money Market Funds [Member]
Class of securities:
Money market funds	43,366	4,548
Level 2
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	10,032	16,264
Total investments fair value	10,032	16,264
U.S. Government Treasury Securities [Member]
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	249	249
U.S. Government Treasury Securities [Member] | Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	249	249
Obligations of U.S. Government Sponsored Enterprises [Member]
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	11,466	59,371
Obligations of U.S. Government Sponsored Enterprises [Member] | Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	4,503	47,489
Obligations of U.S. Government Sponsored Enterprises [Member] | Level 2
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	6,963	11,882
Corporate Debt Securities [Member]
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	7,588	11,415
Corporate Debt Securities [Member] | Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	4,519	7,033
Corporate Debt Securities [Member] | Level 2
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	3,069	4,382
Foreign Corporate Debt Securities [Member]
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	4,759	5,796
Foreign Corporate Debt Securities [Member] | Level 1
Class of securities:
Total fixed-maturity securities, Estimated Fair Value	$ 4,759	$ 5,796