Debt - Additional Information (Detail) (USD $)	1 Months Ended		12 Months Ended	1 Months Ended		12 Months Ended		1 Months Ended	12 Months Ended		1 Months Ended			12 Months Ended			1 Months Ended
	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2012 Family Heritage	Oct. 24, 2012 7.1% Trust Preferred Securities	Sep. 24, 2012 Senior Notes, Due 9/15/22	Dec. 31, 2012 Senior Notes, Due 9/15/22		Sep. 24, 2012 Junior Subordinated Debentures Due 12/15/52	Dec. 31, 2012 Junior Subordinated Debentures Due 12/15/52		Oct. 24, 2012 Junior Subordinated Debentures Due 6/1/46		Dec. 31, 2012 Junior Subordinated Debentures Due 6/1/46	Dec. 31, 2012 Senior Notes, Due 6/15/19		Dec. 31, 2010 Senior Notes, Due 6/15/19 Repurchase	Sep. 24, 2012 Insurance Subsidiary Senior Notes, Due 9/15/22	Sep. 24, 2012 Parent Company
Debt Instrument [Line Items]
Debt due in 2012		$ 319,000,000
Debt due in 2013		0
Debt due in 2014		0
Debt due in 2015		250,000,000
Debt due in 2016		0
Debt due thereafter 2016		753,000,000
Debt issued, principal amount		1,322,489,000			300,000,000	150,000,000	[1],[2]	125,000,000	125,000,000	[3],[4]				292,647,000	[1],[5]
Periodic interest payments due					Semi-annually	3/15 & 9/15	[1],[5]	Quarterly	quarterly	[3],[4]	quarterly	[6],[7]		6/15 & 12/15	[1],[5]
Interest rate					3.80%	3.80%	[1],[5]	5.875%	5.875%	[3],[4]	7.10%	[6],[7]		9.25%	[1],[5]
Commencement date for interest payable					Mar. 15, 2013			Dec. 15, 2012
Senior note acquired by subsidiary																	150,000,000
Proceeds from issuance of debt					147,000,000			121,000,000										297,000,000
Debt instrument spread					0.0030
Issuance Cost								4,200,000
Redemption Period								40 years					40 years
Preferred Securities redeemed				120,000,000
Redemption of preferred securities and accrued dividend				121,000,000
Repayment of Junior Subordinated Debentures											124,000,000
After tax expected loss on repurchase				2,700,000												1,100,000
Debt assumed			20,000,000
Debt instrument, maturity date			Mar. 15, 2036			Sep. 15, 2022	[1],[5]		Dec. 15, 2052	[3],[4]	Jun. 01, 2046	[6],[7]		Jun. 15, 2019	[1],[5]
Debt instrument, Fair Value		1,513,587,000	20,000,000			154,400,000	[1],[5]		126,500,000	[3],[4]				395,703,000	[1],[5]
Debt instrument, amortized cost			20,000,000
Debt instrument, basis spread
Par value repayment of debt																7,400,000
Reacquired principle (book value)																7,300,000
Repayment of debt																8,900,000
Pre-tax loss on repurchase																1,600,000
Line of credit facility limit	600,000,000
Line of credit facility extendable limit	200,000,000
Maximum daily amount letters of credit facility	$ 250,000,000	$ 250,000,000

[1] Callable subject to "make-whole" premium.

[2] The net loss for benefit plans other than pensions reduces other comprehensive income.

[3] Quarterly payments on the 15th of March, June, Sept., and Dec.

[4] Callable as of December 15, 2017.

[5] All securities other than the Junior Subordinated Debentures have equal priority with one another.

[6] Junior Subordinated Debentures are classified as "Due to affiliates" and are junior to other securities in priority of payment.

[7] Called October 24, 2012.