Investments - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Investment [Line Items]
Level 3 Proportion to fixed maturities and equity securities	2.30%		2.30%		2.10%
Other-than-temporary impairments	$ 0	$ 0	$ 2,678,000	$ 0
Total issues of fixed-maturities and equities	1,615		1,615		1,630
Balances related to bifurcated credit loss positions included in other comprehensive income	22,000,000		22,000,000		22,000,000
Loss In Excess Of Other Than Temporary Impairment [Member]
Investment [Line Items]
Loss on sale of real estate pretax			245,000
Loss on sale of real estate, after tax			159,000
Other Than Temporary Impairment [Member]
Investment [Line Items]
Other-than-temporary impairments			0	0
Real Estate [Member]
Investment [Line Items]
Other-than-temporary impairments			2,700,000
Other-than-temporary impairments, after tax			$ 1,700,000