Roll-Forward of Other-Than-Temporary Impairments where Portion Attributable to Non-Credit Related Factors Recognized in Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2013	Mar. 31, 2013
Investments Debt And Equity Securities [Abstract]
Gross Other-Than-Temporary Impairments, Beginning Balance	$ (2,039)	$ (1,995)
Additions for credit losses on securities for which an OTTI was not previously recognized	(105)	(44)
Gross Other-Than-Temporary Impairments, Ending Balance	(2,144)	(2,039)
Other-Than-Temporary Impairments Included in Other Comprehensive Loss, Beginning Balance	(1,308)	(1,264)
Additions for credit losses on securities for which an OTTI was not previously recognized	(105)	(44)
Other-Than-Temporary Impairments Included in Other Comprehensive Loss, Ending Balance	1,413	(1,308)
Net Other-Than Temporary Impairments Included in Retained Earnings, Beginning Balance	(731)	(731)
Additions for credit losses on securities for which an OTTI was not previously recognized
Net Other-Than Temporary Impairments Included in Retained Earnings, Ending Balance	$ (731)	$ (731)