Investment Securities - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Estimated Fair Values of Fixed-Maturity Securities (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	$ 49,339	$ 76,912
Total fixed-maturity securities, Gross Unrealized Gains	10	15
Total fixed-maturity securities, Gross Unrealized Losses	(69)	(96)
Total fixed-maturity securities, Estimated Fair Value	49,280	76,831
Unrestricted Fixed-Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	22,128	47,635
Total fixed-maturity securities, Gross Unrealized Losses	(6)	(10)
Total fixed-maturity securities, Estimated Fair Value	22,122	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	27,211	29,277
Total fixed-maturity securities, Gross Unrealized Gains	10	15
Total fixed-maturity securities, Gross Unrealized Losses	(63)	(86)
Total fixed-maturity securities, Estimated Fair Value	27,158	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	34,469	59,450
Total fixed-maturity securities, Gross Unrealized Gains	1	1
Total fixed-maturity securities, Gross Unrealized Losses	(54)	(80)
Total fixed-maturity securities, Estimated Fair Value	34,416	59,371
Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	9,851	11,415
Total fixed-maturity securities, Gross Unrealized Gains	7	9
Total fixed-maturity securities, Gross Unrealized Losses	(10)	(9)
Total fixed-maturity securities, Estimated Fair Value	9,848	11,415
Foreign Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total fixed-maturity securities, Amortized Cost	4,770	5,798
Total fixed-maturity securities, Gross Unrealized Gains	2	5
Total fixed-maturity securities, Gross Unrealized Losses	(5)	(7)
Total fixed-maturity securities, Estimated Fair Value	$ 4,767	$ 5,796

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