Increase (Decrease) in Carrying Amount of Value of Business Acquired (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition, Acquisition Related Costs [Line Items]
Adjustment related to realized (gains) losses on investments	$ 84	$ 4,711	$ 8,970	$ 6,926
Adjustment related to unrealized (gains) losses and OTTI on investments	(6,319)	780	(19,391)	4,739
VOBA
Business Acquisition, Acquisition Related Costs [Line Items]
Accretion (amortization) expense	(1,646)	(2,651)	(7,499)	(7,988)
Unlocking	(163)	(8,644)	(3,737)	(8,525)
Adjustment related to realized (gains) losses on investments	(9)	(378)	(94)	(611)
Adjustment related to unrealized (gains) losses and OTTI on investments	6,319	(780)	19,391	(4,739)
Increase (decrease) in VOBA carrying amount	$ 4,501	$ (12,453)	$ 8,061	$ (21,863)