Business Segment's Contribution to Select Statements of Income (Loss) Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Policy charge revenue	$ 37,207	$ 37,476
Net investment income (loss)	23,997	27,944
Net realized investment gains (losses)	11,774	31
Derivative gains (losses)	(10,866)	(24,228)
Total Revenues	62,112	41,223
Interest credited to policyholder liabilities	15,733	12,983
Policy benefits (net of reinsurance recoveries)	22,217	(9,490)
Amortization (accretion) of DAC	1,290	1,132
Amortization (accretion) of VOBA	2,919	2,364
Insurance, general and administrative expenses	7,461	8,843
Total Benefits and Expenses	49,620	15,832
Income (Loss) Before Taxes	12,492	25,391
Income tax expense (benefit)	527	575
Net Income (Loss)	11,965	24,816
Operating Segments | Annuity
Segment Reporting Information [Line Items]
Policy charge revenue	23,685	24,011
Net investment income (loss)	11,274	14,230
Net realized investment gains (losses)	10,900	(198)
Derivative gains (losses)	(10,635)	(24,228)
Total Revenues	35,224	13,815
Interest credited to policyholder liabilities	4,944	1,686
Policy benefits (net of reinsurance recoveries)	9,596	(16,121)
Amortization (accretion) of DAC	1,290	1,132
Amortization (accretion) of VOBA	3,360	1,623
Insurance, general and administrative expenses	6,690	8,123
Total Benefits and Expenses	25,880	(3,557)
Income (Loss) Before Taxes	9,344	17,372
Income tax expense (benefit)	394	393
Net Income (Loss)	8,950	16,979
Operating Segments | Life Insurance
Segment Reporting Information [Line Items]
Policy charge revenue	13,522	13,465
Net investment income (loss)	12,723	13,714
Net realized investment gains (losses)	874	229
Derivative gains (losses)	(231)	0
Total Revenues	26,888	27,408
Interest credited to policyholder liabilities	10,789	11,297
Policy benefits (net of reinsurance recoveries)	12,621	6,631
Amortization (accretion) of DAC	0	0
Amortization (accretion) of VOBA	(441)	741
Insurance, general and administrative expenses	771	720
Total Benefits and Expenses	23,740	19,389
Income (Loss) Before Taxes	3,148	8,019
Income tax expense (benefit)	133	182
Net Income (Loss)	$ 3,015	$ 7,837