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Amount of gain (loss) recognized in earnings, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

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- Definition

Amount of gain (loss) recognized in other comprehensive income, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

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- Definition

Purchases that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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- Definition

Sales that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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- Definition

Transfers into assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

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- Definition

Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Reconciliation for Assets Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended			3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2011 Chaucer acquisition	Sep. 30, 2011 Chaucer acquisition	Sep. 30, 2012 Fixed Maturities	Sep. 30, 2011 Fixed Maturities	Sep. 30, 2012 Fixed Maturities	Sep. 30, 2011 Fixed Maturities	Sep. 30, 2011 Fixed Maturities Chaucer acquisition	Sep. 30, 2011 Fixed Maturities Chaucer acquisition	Sep. 30, 2012 Fixed Maturities Municipal	Sep. 30, 2011 Fixed Maturities Municipal	Sep. 30, 2012 Fixed Maturities Municipal	Sep. 30, 2011 Fixed Maturities Municipal	Sep. 30, 2012 Fixed Maturities Corporate	Sep. 30, 2011 Fixed Maturities Corporate	Sep. 30, 2012 Fixed Maturities Corporate	Sep. 30, 2011 Fixed Maturities Corporate	Sep. 30, 2011 Fixed Maturities Corporate Chaucer acquisition	Sep. 30, 2011 Fixed Maturities Corporate Chaucer acquisition	Sep. 30, 2012 Fixed Maturities Residential Mortgage-Backed	Sep. 30, 2011 Fixed Maturities Residential Mortgage-Backed	Sep. 30, 2012 Fixed Maturities Residential Mortgage-Backed	Sep. 30, 2011 Fixed Maturities Residential Mortgage-Backed	Sep. 30, 2011 Fixed Maturities Residential Mortgage-Backed Chaucer acquisition	Sep. 30, 2011 Fixed Maturities Residential Mortgage-Backed Chaucer acquisition	Sep. 30, 2012 Fixed Maturities Commercial Mortgage-Backed	Sep. 30, 2011 Fixed Maturities Commercial Mortgage-Backed	Sep. 30, 2012 Fixed Maturities Commercial Mortgage-Backed	Sep. 30, 2011 Fixed Maturities Commercial Mortgage-Backed	Sep. 30, 2011 Fixed Maturities Asset-Backed	Sep. 30, 2012 Fixed Maturities Asset-Backed	Sep. 30, 2011 Fixed Maturities Asset-Backed	Jun. 30, 2012 Fixed Maturities Asset-Backed	Sep. 30, 2011 Fixed Maturities Asset-Backed Chaucer acquisition	Sep. 30, 2011 Fixed Maturities Asset-Backed Chaucer acquisition	Sep. 30, 2012 Equities and Other	Sep. 30, 2011 Equities and Other	Sep. 30, 2012 Equities and Other	Sep. 30, 2011 Equities and Other	Sep. 30, 2011 Equities and Other Chaucer acquisition	Sep. 30, 2011 Equities and Other Chaucer acquisition
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	$ 102.6	$ 78.3	$ 102.5	$ 70.9			$ 73.4	$ 72.0	$ 75.5	$ 64.6			$ 16.9	$ 16.1	$ 13.6	$ 16.6	$ 27.4	$ 36.8	$ 23.8	$ 28.2			$ 0.6	$ 0.5	$ 5.2	$ 0.8			$ 27.4	$ 18.6	$ 23.7	$ 19.0		$ 9.2		$ 1.1			$ 29.2	$ 6.3	$ 27.0	$ 6.3
Transfers into Level 3	2.6	6.9	7.0	10.6			2.6	6.9	6.9	10.6			2.6		2.6			6.9	4.3	10.6																					0.1
Transfer out of Level 3		(9.3)	(10.8)	(15.8)				(9.3)	(10.8)	(15.8)								(8.8)	(2.1)	(15.3)				(0.5)		(0.5)								(8.7)
Included in earnings	0.1	0.1	0.2	(0.4)			0.1	0.1	0.4	0.1							0.1	0.1	0.4	0.1																					(0.2)	(0.5)
Included in other comprehensive income- net appreciation (depreciation) on available for sale securities	(0.8)	(2.1)	2.8	(0.9)			0.9	(0.5)	1.5	0.2			0.3		1.0	0.1		(0.3)	0.5						0.1				0.6	0.1	(0.1)	0.4	(0.3)		(0.3)				(1.7)	(1.6)	1.3	(1.1)
Purchases	0.1	7.3	10.8	19.1	38.7	38.7	0.1	7.3	10.8	19.1	14.5	14.5			3.0				1.5	11.8	0.1	0.1	0.1		0.1		5.6	5.6		7.3	5.2	7.3		1.0			8.8	8.8					24.2	24.2
Sales	(0.9)	(13.2)	(8.8)	(15.5)			(0.9)	(13.2)	(8.1)	(15.5)			(0.2)	(0.3)	(0.6)	(0.9)	(0.1)	(12.3)	(1.0)	(13.0)				(0.1)	(4.7)	(0.4)			(0.6)	(0.4)	(1.4)	(1.1)	(0.1)	(0.4)	(0.1)						(0.7)
Ending Balance	$ 103.7	$ 106.7	$ 103.7	$ 106.7			$ 76.2	$ 77.8	$ 76.2	$ 77.8			$ 19.6	$ 15.8	$ 19.6	$ 15.8	$ 27.4	$ 22.5	$ 27.4	$ 22.5			$ 0.7	$ 5.5	$ 0.7	$ 5.5			$ 27.4	$ 25.6	$ 27.4	$ 25.6	$ 8.4	$ 1.1	$ 8.4	$ 1.1			$ 27.5	$ 28.9	$ 27.5	$ 28.9