Disclosures About Fair Value Of Financial Instruments (Summary Of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	$ 519.8	$ 377.0
Fair Value	443.1	298.2
Junior Subordinated Debentures [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	311.5	311.5
Fair Value	252.2	250.8
Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	143.8	0
Fair Value	143.8	0
Other Indebtedness [Member] | Floating Rate Loan Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	63.7	64.7
Fair Value	46.5	46.8
Other Indebtedness [Member] | Notes Payable, Other Payables [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	0.8	0.8
Fair Value	$ 0.6	$ 0.6