Business Segment's Contribution to Select Statements of Income (Loss) Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Policy charge revenue	$ 36,180	$ 37,369	$ 73,387	$ 74,845
Net investment income (loss)	22,502	26,417	46,499	54,361
Net realized investment gains (losses)	(2,888)	2,184	8,886	2,215
Derivative gains (losses)	(15,610)	(6,540)	(26,476)	(30,768)
Total Revenues	40,184	59,430	102,296	100,653
Interest credited to policyholder liabilities	12,441	13,370	28,174	26,353
Policy benefits (net of reinsurance recoveries)	14,159	11,889	36,376	2,399
Amortization (accretion) of DAC	(86)	605	1,204	1,737
Amortization (accretion) of VOBA	6,508	2,854	9,427	5,218
Insurance, general and administrative expenses	9,826	6,577	17,287	15,420
Total Benefits and Expenses	42,848	35,295	92,468	51,127
Income (Loss) Before Taxes	(2,664)	24,135	9,828	49,526
Income tax expense (benefit)	(527)	0	0	575
Net Income (Loss)	(2,137)	24,135	9,828	48,951
Operating Segments | Annuity
Segment Reporting Information [Line Items]
Policy charge revenue	23,398	23,939	47,083	47,950
Net investment income (loss)	10,111	13,023	21,385	27,253
Net realized investment gains (losses)	(2,312)	1,887	8,588	1,689
Derivative gains (losses)	(15,834)	(6,540)	(26,469)	(30,768)
Total Revenues	15,363	32,309	50,587	46,124
Interest credited to policyholder liabilities	1,754	1,847	6,697	3,533
Policy benefits (net of reinsurance recoveries)	3,329	3,941	12,925	(12,180)
Amortization (accretion) of DAC	(86)	605	1,204	1,737
Amortization (accretion) of VOBA	(1,102)	612	2,258	2,235
Insurance, general and administrative expenses	8,867	5,773	15,557	13,896
Total Benefits and Expenses	12,762	12,778	38,641	9,221
Income (Loss) Before Taxes	2,601	19,531	11,946	36,903
Income tax expense (benefit)	(394)	0		393
Net Income (Loss)	2,995	19,531	11,946	36,510
Operating Segments | Life Insurance
Segment Reporting Information [Line Items]
Policy charge revenue	12,782	13,430	26,304	26,895
Net investment income (loss)	12,391	13,394	25,114	27,108
Net realized investment gains (losses)	(576)	297	298	526
Derivative gains (losses)	224	0	(7)
Total Revenues	24,821	27,121	51,709	54,529
Interest credited to policyholder liabilities	10,687	11,523	21,477	22,820
Policy benefits (net of reinsurance recoveries)	10,830	7,948	23,451	14,579
Amortization (accretion) of DAC	0	0
Amortization (accretion) of VOBA	7,610	2,242	7,169	2,983
Insurance, general and administrative expenses	959	804	1,730	1,524
Total Benefits and Expenses	30,086	22,517	53,827	41,906
Income (Loss) Before Taxes	(5,265)	4,604	(2,118)	12,623
Income tax expense (benefit)	(133)	0		182
Net Income (Loss)	$ (5,132)	$ 4,604	$ (2,118)	$ 12,441