Differences in Tax and Estimated Tax Provisions at Weighted Average Tax Rate (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Income Tax [Line Items]
Expected tax provision at weighted average rate, Amount	$ (256)	$ 121	$ 279	$ 6,834
Tax exempt interest, Amount	(372)	(496)	(779)	(1,020)
Dividend exclusion, Amount	(297)	(210)	(532)	(367)
Effective tax rate adjustment, Amount	(1,588)	(1,471)	(4,175)
Other, Amount	16	34	2	55
Income tax expense (benefit), Amount	$ (2,497)	$ (2,022)	$ (5,205)	$ 5,502
Expected tax provision at weighted average rate, % of Pre-Tax Income	(3.60%)	5.30%	1.80%	28.40%
Tax exempt interest, % of Pre-Tax Income	(5.20%)	(21.90%)	(5.10%)	(4.20%)
Dividend exclusion, % of Pre-Tax Income	(4.20%)	(9.30%)	(3.50%)	(1.50%)
Effective tax rate adjustment, % of Pre-Tax Income	(22.30%)	(65.00%)	(27.30%)
Other, % of Pre-Tax Income	0.20%	1.50%		0.20%
Income tax expense (benefit), % of Pre-Tax Income	(35.10%)	(89.40%)	(34.10%)	22.90%