Components of Net Unrealized Gains Losses and Other-Than-Temporary Impairments Included in Accumulated Other Comprehensive Income Net of Taxes (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of taxes	$ 131,674	$ 56,591
Unrealized Holding Gains (Losses) on AFS Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before taxes	153,007	77,924
Unrealized Holding Gains (Losses) on AFS Securities | Fixed maturity AFS securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before taxes	181,297	94,644
Unrealized Holding Gains (Losses) on AFS Securities | Equity AFS securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before taxes	1,279	890
Unrealized Holding Gains (Losses) on AFS Securities | Valuation of business acquired
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before taxes	(34,229)	(21,812)
Unrealized Holding Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before taxes	4,660	4,202
Accumulated Net Unrealized Liability Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before taxes	(21,333)	(21,333)
Accumulated Net Unrealized Liability Gain (Loss) | Federal income taxes - deferred
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before taxes	$ (21,333)	$ (21,333)