Note 4 - Fair Value of Financial Instruments Fair Value Assets Liabilities by Hierarchy Level (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value by Hierarchy Level [Line Items]
Other Invested Assets, Carrying Amount	$ 14,000,000		$ 14,600,000
Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	3,607,600,000	[1]	3,614,700,000	[2]
Total Assets at Fair Value	3,607,600,000		3,614,700,000
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	0				0
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	0				0
US government and agency securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	633,600,000		839,900,000
State and municipal obligations | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	353,000,000		362,800,000
Money market instruments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	601,300,000		600,300,000
Corporate bonds and notes | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	1,115,000,000		992,800,000
RMBS | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	128,100,000		132,300,000
CMBS | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	247,900,000		246,800,000
Other ABS | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	177,600,000		185,500,000
Foreign government securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	35,300,000		37,700,000
Equity securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	214,800,000	[3]	215,600,000	[3]
Other investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	101,000,000	[4]	1,000,000	[5]
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	1,394,500,000	[1]	1,601,200,000	[2]
Total Assets at Fair Value	1,394,500,000		1,601,200,000
Assets Held-for-sale, Long Lived, Fair Value Disclosure	502,100,000		495,100,000
Fair Value, Inputs, Level 1 | US government and agency securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	630,600,000		836,900,000
Fair Value, Inputs, Level 1 | State and municipal obligations | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	0		0
Fair Value, Inputs, Level 1 | Money market instruments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	601,300,000		600,300,000
Fair Value, Inputs, Level 1 | Corporate bonds and notes | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	0		0
Fair Value, Inputs, Level 1 | RMBS | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	0		0
Fair Value, Inputs, Level 1 | CMBS | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	0		0
Fair Value, Inputs, Level 1 | Other ABS | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	0		0
Fair Value, Inputs, Level 1 | Foreign government securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	0		0
Fair Value, Inputs, Level 1 | Equity securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	162,600,000	[3]	164,000,000	[3]
Fair Value, Inputs, Level 1 | Other investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	0	[4]	0	[5]
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	2,213,100,000	[1]	2,013,500,000	[2]
Total Assets at Fair Value	2,213,100,000		2,013,500,000
Assets Held-for-sale, Long Lived, Fair Value Disclosure	838,000,000		839,200,000
Fair Value, Inputs, Level 2 | US government and agency securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	3,000,000		3,000,000
Fair Value, Inputs, Level 2 | State and municipal obligations | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	353,000,000		362,800,000
Fair Value, Inputs, Level 2 | Money market instruments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	0		0
Fair Value, Inputs, Level 2 | Corporate bonds and notes | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	1,115,000,000		992,800,000
Fair Value, Inputs, Level 2 | RMBS | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	128,100,000		132,300,000
Fair Value, Inputs, Level 2 | CMBS | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	247,900,000		246,800,000
Fair Value, Inputs, Level 2 | Other ABS | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	177,600,000		185,500,000
Fair Value, Inputs, Level 2 | Foreign government securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	35,300,000		37,700,000
Fair Value, Inputs, Level 2 | Equity securities | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	52,200,000	[3]	51,600,000	[3]
Fair Value, Inputs, Level 2 | Other investments | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	101,000,000	[4]	1,000,000	[5]
Fair Value, Inputs, Level 2 | Trust Preferred Securities [Member] | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	100,000,000
Fair Value, Inputs, Level 2 | Short Term CDs | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Investments at Fair Value	1,000,000
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Fair Value by Hierarchy Level [Line Items]
Total Assets at Fair Value	0		0
Assets Held-for-sale, Long Lived, Fair Value Disclosure	102,800,000		102,600,000
Variable Interest Entity Debt			$ 3,800,000
Total Level III Liabilities			100.00%

[1] Does not include certain other invested assets ($14.0 million), primarily invested in limited partnerships, accounted for as cost-method investments and not measured at fair value. Also excludes investments classified as assets held for sale of $502.1 million, $838.0 million and $102.8 million, with fair values categorized in Level I, Level II and Level III, respectively.

[2] Does not include certain other invested assets ($14.6 million), primarily invested in limited partnerships, accounted for as cost-method investments and not measured at fair value. Also excludes investments classified as assets held for sale of $495.1 million, $839.2 million and $102.6 million, with fair values categorized in Level I, Level II and Level III, respectively.

[3] Comprising broadly diversified domestic equity mutual funds and certain common stocks included within Level I and various preferred stocks invested across numerous companies and industries included within Level II.

[4] Comprising short-term certificates of deposit ($1.0 million) and short-term commercial paper ($100.0 million) included within Level II.

[5] Comprising short-term certificates of deposit.