Schedule II - Condensed Financial Information of Registrant (Notes To Condensed Financial Statements) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Dividends from subsidiaries	$ 478,840,000	$ 488,376,000	$ 436,814,000
Stock-based compensation not involving cash	32,203,000	25,642,000	21,605,000
Debt assumed to acquire Family Heritage	0	0	20,000,000
Interest paid	77,066,000	81,322,000	77,686,000
Income taxes received	112,935,000	139,091,000	89,061,000
Preferred stock, shares issued	0	0	0	0
Preferred stock, shares outstanding	0	0
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Stock-based compensation not involving cash	32,203,000	25,642,000	21,605,000
Debt assumed to acquire Family Heritage	0	0	20,000,000
Dividend of subsidiary to Parent	0	1,246,557,000	0
Dividend of subsidiary applied to loan balance	0	72,000,000	0
Interest paid	77,663,000	85,443,000	76,833,000
Income taxes received	25,581,000	27,820,000	29,251,000
Preferred stock, liquidation distribution available to stockholders, per share in thousands	$ 1,000
Preferred stock, liquidating distribution legally available, aggregate value	$ 351,000,000
Cumulative Series A Preferred Stock [Member] | Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Preferred stock, shares issued	351,000
Preferred stock, shares outstanding	351,000
6.50% Cumulative Preferred Stock, Series A [Member] | Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Preferred stock, shares issued	280,000
Preferred stock, shares outstanding	280,000
Preferred stock, dividend rate, percentage	6.50%
7.15% Cumulative Preferred Stock, Series A [Member] | Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Preferred stock, shares issued	71,000
Preferred stock, shares outstanding	71,000
Preferred stock, dividend rate, percentage	7.15%