Increase (Decrease) in Carrying Amount of Value of Business Acquired (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Acquisition, Acquisition Related Costs [Line Items]
Adjustment related to realized (gains) losses on investments	$ (2,888)	$ 2,184	$ 8,886	$ 2,215
Adjustment related to unrealized (gains) losses and OTTI on investments	(4,288)	3,088	(13,072)	3,959
VOBA
Business Acquisition, Acquisition Related Costs [Line Items]
Accretion (amortization) expense	(2,988)	(3,110)	(5,853)	(5,337)
Unlocking	(3,520)	256	(3,574)	119
Adjustment related to realized (gains) losses on investments	(12)	(129)	(85)	(233)
Adjustment related to unrealized (gains) losses and OTTI on investments	4,288	(3,088)	13,072	(3,959)
Increase (decrease) in VOBA carrying amount	$ (2,232)	$ (6,071)	$ 3,560	$ (9,410)