Summary of Activity Related to Other-Than-Temporary Impairment Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2012 Investment	Jun. 30, 2013 Investment	Jun. 30, 2012 Investment
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Number of Securities	2	2	4
Total other-than-temporary impairment losses	$ 496	$ 42	$ 693
Portion of loss recognized in other comprehensive income			43
Net other-than-temporary impairment losses recognized in earnings	496	42	650
Residential Mortgage Backed Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Number of Securities			1
Total other-than-temporary impairment losses			54
Portion of loss recognized in other comprehensive income			43
Net other-than-temporary impairment losses recognized in earnings			11
Equity Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Number of Securities	2	2	3
Total other-than-temporary impairment losses	496	42	639
Net other-than-temporary impairment losses recognized in earnings	$ 496	$ 42	$ 639