Investment Securities - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Estimated Fair Values of Fixed-Maturity Securities (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	$ 24,115	$ 76,912
Total fixed-maturity securities, Gross Unrealized Gains	3	15
Total fixed-maturity securities, Gross Unrealized Losses	(56)	(96)
Total fixed-maturity securities, Estimated Fair Value	24,062	76,831
Unrestricted Fixed-Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	1,704	47,635
Total fixed-maturity securities, Gross Unrealized Losses	(4)	(10)
Total fixed-maturity securities, Estimated Fair Value	1,700	47,625	[1]
Fixed-Maturity Securities Held in Trust [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	22,411	29,277
Total fixed-maturity securities, Gross Unrealized Gains	3	15
Total fixed-maturity securities, Gross Unrealized Losses	(52)	(86)
Total fixed-maturity securities, Estimated Fair Value	22,362	29,206	[1]
U.S. Government Treasury Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	249	249
Total fixed-maturity securities, Estimated Fair Value	249	249
Obligations of U.S. Government Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	11,512	59,450
Total fixed-maturity securities, Gross Unrealized Gains		1
Total fixed-maturity securities, Gross Unrealized Losses	(46)	(80)
Total fixed-maturity securities, Estimated Fair Value	11,466	59,371
Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	7,596	11,415
Total fixed-maturity securities, Gross Unrealized Gains	1	9
Total fixed-maturity securities, Gross Unrealized Losses	(9)	(9)
Total fixed-maturity securities, Estimated Fair Value	7,588	11,415
Foreign Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	4,758	5,798
Total fixed-maturity securities, Gross Unrealized Gains	2	5
Total fixed-maturity securities, Gross Unrealized Losses	(1)	(7)
Total fixed-maturity securities, Estimated Fair Value	$ 4,759	$ 5,796

[1] Balances derived from audited financial statements as of December 31, 2016.