Net Investment Income (Loss) By Source (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net Investment Income [Line Items]
Gross investment income	$ 27,926	$ 29,484	$ 57,092	$ 57,057
Less investment expenses	(1,509)	(1,870)	(2,731)	(2,991)
Net investment income (loss)	26,417	27,614	54,361	54,066
Limited partnership
Net Investment Income [Line Items]
Gross investment income	279	(90)	1,943	(2,631)
Fixed maturity AFS securities
Net Investment Income [Line Items]
Gross investment income	15,204	16,863	30,668	34,230
Equity AFS securities
Net Investment Income [Line Items]
Gross investment income	422	538	840	1,003
Mortgage loans on real estate
Net Investment Income [Line Items]
Gross investment income	1,400	1,264	2,863	2,467
Policy loans
Net Investment Income [Line Items]
Gross investment income	8,234	8,382	16,454	16,991
Derivatives
Net Investment Income [Line Items]
Gross investment income	1,684	1,857	3,274	3,769
Cash and Cash Equivalents
Net Investment Income [Line Items]
Gross investment income	633	564	907	1,015
Other
Net Investment Income [Line Items]
Gross investment income	$ 70	$ 106	$ 143	$ 213