Investment Securities - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Estimated Fair Values of Fixed-Maturity Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	$ 3,674	$ 76,912
Total fixed-maturity securities, Gross Unrealized Gains		15
Total fixed-maturity securities, Gross Unrealized Losses	(14)	(96)
Total fixed-maturity securities, Estimated Fair Value	3,660	76,831
Unrestricted Fixed-Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	2,151	47,635
Total fixed-maturity securities, Gross Unrealized Losses	(9)	(10)
Total fixed-maturity securities, Estimated Fair Value	2,142	47,625
Fixed-Maturity Securities Held in Trust [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	1,523	29,277
Total fixed-maturity securities, Gross Unrealized Gains		15
Total fixed-maturity securities, Gross Unrealized Losses	(5)	(86)
Total fixed-maturity securities, Estimated Fair Value	1,518	29,206
U.S. Government Treasury Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost		249
Total fixed-maturity securities, Estimated Fair Value		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	2,249	59,450
Total fixed-maturity securities, Gross Unrealized Gains		1
Total fixed-maturity securities, Gross Unrealized Losses	(10)	(80)
Total fixed-maturity securities, Estimated Fair Value	2,239	59,371
Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	1,425	11,415
Total fixed-maturity securities, Gross Unrealized Gains		9
Total fixed-maturity securities, Gross Unrealized Losses	(4)	(9)
Total fixed-maturity securities, Estimated Fair Value	$ 1,421	11,415
Foreign Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost		5,798
Total fixed-maturity securities, Gross Unrealized Gains		5
Total fixed-maturity securities, Gross Unrealized Losses		(7)
Total fixed-maturity securities, Estimated Fair Value		$ 5,796