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Variable Interest Entities (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($) trust	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) trust director	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured	15.00%								15.00%
Accumulated losses	$ 3,084.9				$ 3,010.5				$ 3,084.9	$ 3,010.5
Noncontrolling interest in VIE	454.8				542.7				454.8	542.7
Non-controlling interest in consolidated subsidiaries	$ 6.1	$ (16.0)	$ (0.9)	$ (7.3)	(15.0)	$ (11.2)	$ 4.6	$ (0.6)	(18.1)	(22.2)	$ (12.5)
Payments to Acquire Other Investments									$ 78.0	114.7	$ 22.0
HG Global
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured	15.00%								15.00%
Noncontrolling interest in VIE	$ 17.1				17.9				$ 17.1	17.9
Star & Shield Insurance Exchange [Member]
Variable Interest Entity [Line Items]
Surplus notes	21.0								21.0
Total assets related to consolidated VIE's	14.2				13.5				14.2	13.5
Total liabilities related to consolidated VIE's	30.3				25.9				30.3	25.9
Accumulated losses	16.0								$ 16.0
Prospector
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage									67.60%
Houston General Insurance [Member]
Variable Interest Entity [Line Items]
Surplus notes	5.0								$ 5.0
Total assets related to consolidated VIE's	5.1				2.4				5.1	2.4
Total liabilities related to consolidated VIE's	5.0				4.0				5.0	4.0
Accumulated losses	0.2								0.2
Accrued interest on surplus notes	$ 0.3								$ 0.3
Common Stock | BAM
Variable Interest Entity [Line Items]
Issuance of notes												$ 503.0
BAM
Variable Interest Entity [Line Items]
Right to elect directors on board number | director									2
HG Global
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured	15.00%								15.00%
Surplus notes												$ 503.0
Noncontrolling interest in VIE	$ 17.1				$ 17.9				$ 17.1	$ 17.9
First Loss Reinsurance Treaty [Member] | HG Global
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured	15.00%								15.00%
First Loss Reinsurance Treaty [Member] | BAM
Variable Interest Entity [Line Items]
Percentage of Premiums	60.00%								60.00%
First Loss Reinsurance Treaty [Member] | HG Global
Variable Interest Entity [Line Items]
Number of Trust | trust	2								2
Amendment [Member] | Houston General Insurance [Member]
Variable Interest Entity [Line Items]
Surplus notes	$ 5.0								$ 5.0

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