Investments - Progression of Credit-Related Portion of OTTI on Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments Debt And Equity Securities [Abstract]
Beginning balance	$ (2,632)	$ (2,632)	$ (2,666)
Additional credit impairments on:
Previously impaired securities	0	0	(61)
Securities without previous impairments	0	0	0
Total additional credit impairments securities	0	0	(61)
Reductions for securities deemed worthless (realized)	0	0	95
Ending balance	$ (2,632)	$ (2,632)	$ (2,632)