Business Segment's Contribution to Select Statements of Income (Loss) Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Policy charge revenue	$ 35,978	$ 37,454	$ 109,365	$ 112,299
Net investment income (loss)	22,364	27,427	68,863	81,788
Net realized investment gains (losses)	84	4,711	8,970	6,926
Derivative gains (losses)	(15,168)	(9,239)	(41,644)	(40,007)
Total Revenues	43,258	60,353	145,554	161,006
Interest credited to policyholder liabilities	12,661	13,207	40,835	39,560
Policy benefits (net of reinsurance recoveries)	(2,403)	(963)	33,973	1,436
Amortization (accretion) of DAC	1,200	1,139	2,404	2,876
Amortization (accretion) of VOBA	1,809	11,295	11,236	16,513
Insurance, general and administrative expenses	9,542	9,739	26,829	25,159
Total Benefits and Expenses	22,809	34,417	115,277	85,544
Income (Loss) Before Taxes	20,449	25,936	30,277	75,462
Income tax expense (benefit)	0	0	0	575
Net Income (Loss)	20,449	25,936	30,277	74,887
Operating Segments | Annuity
Segment Reporting Information [Line Items]
Policy charge revenue	22,891	23,954	69,974	71,904
Net investment income (loss)	9,875	13,741	31,260	40,994
Net realized investment gains (losses)	60	3,558	8,648	5,247
Derivative gains (losses)	(15,165)	(9,239)	(41,632)	(40,007)
Total Revenues	17,661	32,014	68,250	78,138
Interest credited to policyholder liabilities	1,678	2,140	8,375	5,673
Policy benefits (net of reinsurance recoveries)	(6,874)	(9,261)	6,051	(21,441)
Amortization (accretion) of DAC	1,200	1,139	2,404	2,876
Amortization (accretion) of VOBA	1,850	1,011	4,108	3,246
Insurance, general and administrative expenses	8,858	9,041	24,415	22,937
Total Benefits and Expenses	6,712	4,070	45,353	13,291
Income (Loss) Before Taxes	10,949	27,944	22,897	64,847
Income tax expense (benefit)	0	0		393
Net Income (Loss)	10,949	27,944	22,897	64,454
Operating Segments | Life Insurance
Segment Reporting Information [Line Items]
Policy charge revenue	13,087	13,500	39,391	40,395
Net investment income (loss)	12,489	13,686	37,603	40,794
Net realized investment gains (losses)	24	1,153	322	1,679
Derivative gains (losses)	(3)	0	(12)
Total Revenues	25,597	28,339	77,304	82,868
Interest credited to policyholder liabilities	10,983	11,067	32,460	33,887
Policy benefits (net of reinsurance recoveries)	4,471	8,298	27,922	22,877
Amortization (accretion) of DAC	0	0
Amortization (accretion) of VOBA	(41)	10,284	7,128	13,267
Insurance, general and administrative expenses	684	698	2,414	2,222
Total Benefits and Expenses	16,097	30,347	69,924	72,253
Income (Loss) Before Taxes	9,500	(2,008)	7,380	10,615
Income tax expense (benefit)	0	0		182
Net Income (Loss)	$ 9,500	$ (2,008)	$ 7,380	$ 10,433