Schedule II. Condensed Financial Information of Registrant (Notes To Condensed Financial Statements) (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Stock-based compensation not involving cash	$ 44,843	$ 39,792	$ 37,034
Interest paid	81,723	83,518	82,494
Income taxes paid (received)	$ 101,982	$ 91,510	74,379
Preferred stock, shares outstanding (in shares)	0	0
Parent Company
Condensed Financial Statements, Captions [Line Items]
Cash dividends from subsidiaries	$ 479,988	$ 448,142	453,904
Stock-based compensation not involving cash	44,843	39,792	37,034
Investment in subsidiaries	0	11,899	317,027
Dividend of property to Parent	0	11,889	0
Interest paid	86,868	86,982	86,606
Income taxes paid (received)	$ (16,617)	$ (21,377)	$ (19,961)
Preferred stock, liquidation distribution available to stockholders, per share in thousands (in dollars per share)	$ 1,000
Preferred stock, liquidating distribution legally available, aggregate value	$ 351,000
Cumulative Series A Preferred Stock | Parent Company
Condensed Financial Statements, Captions [Line Items]
Preferred stock, shares issued (in shares)	351,000
Preferred stock, shares outstanding (in shares)	351,000
6.50% Cumulative Preferred Stock, Series A | Parent Company
Condensed Financial Statements, Captions [Line Items]
Preferred stock, shares issued (in shares)	280,000
Preferred stock, shares outstanding (in shares)	280,000
Preferred stock, dividend rate, percentage	6.50%
7.15% Cumulative Preferred Stock, Series A | Parent Company
Condensed Financial Statements, Captions [Line Items]
Preferred stock, shares issued (in shares)	71,000
Preferred stock, shares outstanding (in shares)	71,000
Preferred stock, dividend rate, percentage	7.15%