Investments - Progression of Credit-Related Portion of OTTI on Investments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Amortized Cost And Fair Value Debt Securities [Abstract]
Beginning balance	$ (2,607)	$ (3,426)	$ (2,666)	$ (3,425)
Additional credit impairments on:
Previously impaired securities		(15)	(28)	(16)
Securities without previous impairments
Total additional credit impairments securities		(15)	(28)	(16)
Reductions for securities sold (realized)	(8)		(95)
Ending balance	$ (2,599)	$ (3,441)	$ (2,599)	$ (3,441)