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Fair Value Measurements - Fair Value Inputs (Details) (USD $) In Millions, unless otherwise specified
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Mar. 31, 2012
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Dec. 31, 2011
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Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Trading Securities, Fair Value Disclosure |
$ 4.6 |
$ 4.4 |
| Investments, Fair Value Disclosure |
5,221.9 |
5,175.1 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Fixed Maturities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
4,787.7 |
4,773.4 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | US Government and Government Agencies and Authorities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
474.4 |
491.7 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | States and Political Subdivisions [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
1,825.4 |
1,852.6 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Bonds and Notes [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
2,401.5 |
2,342.3 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Redeemable Preferred Stocks [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
81.4 |
81.7 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Mortgage and Asset-backed [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
5.0 |
5.1 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Equity Securities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
429.6 |
397.3 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Preferred Stock Finance, Insurance and Real Estate [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
97.4 |
86.7 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Preferred Stocks Other Industries [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
21.2 |
20.5 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Common Stocks Manufacturing [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
87.1 |
83.4 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Common Stock Other Industries [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
49.7 |
47.0 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Exchange Traded Funds [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
67.7 |
66.6 |
|
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Limited Liability Companies and Limited Partnerships [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
106.5 |
93.1 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Trading Securities, Fair Value Disclosure |
4.6 |
4.4 |
| Investments, Fair Value Disclosure |
330.7 |
342.1 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Maturities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
133.1 |
153.6 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government and Government Agencies and Authorities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
133.1 |
153.6 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | States and Political Subdivisions [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Bonds and Notes [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
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Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Redeemable Preferred Stocks [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage and Asset-backed [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
193.0 |
184.1 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Preferred Stock Finance, Insurance and Real Estate [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Preferred Stocks Other Industries [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Common Stocks Manufacturing [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
80.2 |
74.7 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Common Stock Other Industries [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
45.1 |
42.8 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Exchange Traded Funds [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
67.7 |
66.6 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Limited Liability Companies and Limited Partnerships [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Trading Securities, Fair Value Disclosure |
0 |
0 |
| Investments, Fair Value Disclosure |
4,506.6 |
4,484.9 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Maturities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
4,388.8 |
4,378.3 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government and Government Agencies and Authorities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
341.3 |
338.1 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | States and Political Subdivisions [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
1,825.4 |
1,852.6 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Bonds and Notes [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
2,142.3 |
2,107.2 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Redeemable Preferred Stocks [Member]
|
|
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
75.1 |
75.6 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage and Asset-backed [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
4.7 |
4.8 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
117.8 |
106.6 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Preferred Stock Finance, Insurance and Real Estate [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
97.4 |
86.7 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Preferred Stocks Other Industries [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
15.2 |
14.9 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Common Stocks Manufacturing [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
5.2 |
5.0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Common Stock Other Industries [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Exchange Traded Funds [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Limited Liability Companies and Limited Partnerships [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Trading Securities, Fair Value Disclosure |
0 |
0 |
| Investments, Fair Value Disclosure |
384.6 |
348.1 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
265.8 |
241.5 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government and Government Agencies and Authorities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | States and Political Subdivisions [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Bonds and Notes [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
259.2 |
235.1 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Redeemable Preferred Stocks [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
6.3 |
6.1 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage and Asset-backed [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
0.3 |
0.3 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
118.8 |
106.6 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Preferred Stock Finance, Insurance and Real Estate [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Preferred Stocks Other Industries [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
6.0 |
5.6 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Common Stocks Manufacturing [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
1.7 |
3.7 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Common Stock Other Industries [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
4.6 |
4.2 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Exchange Traded Funds [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
0 |
0 |
|
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Limited Liability Companies and Limited Partnerships [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Available-for-sale Securities, Fair Value Disclosure |
106.5 |
93.1 |
|
Private Equity Funds and Mezzanine Debt Funds [Member] | Fair Value, Inputs, Level 3 [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments |
$ 90.6 |
|