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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.

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