Components of Other-Than-Temporary Impairments Reflected in Statements of Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI Losses on Securities	$ 0	$ 1,015	$ 0	$ 4,684
Net OTTI Losses Recognized in OCI	0	0	0	0
Net OTTI Losses Recognized in Income	0	1,015	0	4,684
Gross OTTI losses
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI Losses on Securities	0	1,544	0	5,213
Net OTTI Losses Recognized in OCI	0	0	0	0
Net OTTI Losses Recognized in Income	0	1,544	0	5,213
Value of business acquired amortization
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI Losses on Securities	0	(529)	0	(529)
Net OTTI Losses Recognized in OCI	0	0	0	0
Net OTTI Losses Recognized in Income	$ 0	$ (529)	$ 0	$ (529)