Investments - Progression of Credit-Related Portion of OTTI on Investments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Roll Forward]
Beginning balance	$ (2,599)	$ (3,441)	$ (2,666)	$ (3,425)
Additional credit impairments on:
Previously impaired securities	(33)	(7)	(61)	(23)
Securities without previous impairments
Total additional credit impairments securities	(33)	(7)	(61)	(23)
Reductions for securities sold (realized)			(95)
Ending balance	$ (2,632)	$ (3,448)	$ (2,632)	$ (3,448)