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, 2012	Mar. 31, 2012
Gross Other-Than-Temporary Impairments
Gross Other-Than-Temporary Impairments, Beginning Balance	$ (2,732)	$ (2,707)
Additions for credit losses on securities for which an OTTI was not previously recognized	(20)	(25)
Gross Other-Than-Temporary Impairments, Ending Balance	(2,752)	(2,732)
Other-Than-Temporary Impairments Included in Other Comprehensive Loss
Other-Than-Temporary Impairments Included in Other Comprehensive Loss, Beginning Balance	(2,001)	(2,053)
Additions for credit losses on securities for which an OTTI was not previously recognized	(20)	52
Other-Than-Temporary Impairments Included in Other Comprehensive Loss, Ending Balance	(2,021)	(2,001)
Net Other-Than Temporary Impairments Included in Retained Earnings
Net Other-Than Temporary Impairments Included in Retained Earnings, Beginning Balance	(731)	(654)
Additions for credit losses on securities for which an OTTI was not previously recognized		(77)
Net Other-Than Temporary Impairments Included in Retained Earnings, Ending Balance	$ (731)	$ (731)