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Investment Securities (Fair Value Measurement by Level) (Details) - USD ($) $ in Thousands | Mar. 31, 2016 | Dec. 31, 2015 | Mar. 31, 2015 | Dec. 31, 2014
--- | --- | --- | --- | ---
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | $ 3,360,200 | $ 4,050,900 | $ 3,355,300 | $ 3,343,600
Other Investments | 321,800 | 315,800 |  |
Short-term investments, at amortized cost (which approximates fair value) | 261,700 | 211,300 |  |
Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 419,600 | 1,152,200 | 537,000 | 550,600
Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 2,566,100 | 2,531,400 | 2,380,900 | 2,372,900
Debt securities issued by corporations |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 910,400 | 1,000,000 |  |
Mortgage-backed and asset-backed securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 1,260,900 | 1,167,000 |  |
Mortgage-backed and asset-backed securities | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 1,260,900 | 1,167,000 |  |
Mortgage-backed and asset-backed securities | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fixed maturity investments. | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 70,500 | 70,000 | 101,100 | 76,400
Common equity securities | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 | 32,000 | 39,500
Other long-term investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 172,700 | 169,500 | 102,800 | 110,600
Hedge and private equity funds included in other long-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Other long-term investments | 131,300 | 127,800 |  |
Hedge and private equity funds included in other long-term investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 131,300 | 127,800 | 201,500 | 193,600
Fair value measured on a recurring basis |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 3,490,600 | 4,134,400 |  |
Fair value measured on a recurring basis | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 681,300 | 1,363,500 |  |
Fair value measured on a recurring basis | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 2,566,100 | 2,531,400 |  |
Fair value measured on a recurring basis | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 243,200 | 239,500 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 88,800 | 160,000 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 72,300 | 133,400 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 16,500 | 26,600 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 910,400 | 1,000,000 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 910,400 | 1,000,000 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 242,100 | 253,300 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 242,100 | 253,300 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 135,100 | 135,600 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 135,100 | 135,600 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 155,500 | 175,900 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 155,500 | 175,900 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 43,300 | 49,200 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 43,300 | 49,200 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 124,700 | 151,300 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 124,700 | 151,300 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 69,300 | 82,000 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 69,300 | 82,000 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 57,100 | 60,000 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 57,100 | 60,000 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 57,200 | 61,500 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 57,200 | 61,500 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 26,100 | 31,200 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 26,100 | 31,200 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 1,260,900 | 1,167,000 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 1,260,900 | 1,167,000 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Municipal obligations |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 268,700 | 228,800 |  |
Fair value measured on a recurring basis | Municipal obligations | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Municipal obligations | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 268,700 | 228,800 |  |
Fair value measured on a recurring basis | Municipal obligations | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 1,200 | 1,200 |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 600 | 600 |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 600 | 600 |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Preferred Stock |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 83,200 | 82,700 |  |
Fair value measured on a recurring basis | Preferred Stock | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Preferred Stock | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 12,700 | 12,700 |  |
Fair value measured on a recurring basis | Preferred Stock | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 70,500 | 70,000 |  |
Fair value measured on a recurring basis | Fixed maturity investments. |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 2,613,200 | 2,639,700 |  |
Fair value measured on a recurring basis | Fixed maturity investments. | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 72,900 | 134,000 |  |
Fair value measured on a recurring basis | Fixed maturity investments. | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 2,469,800 | 2,435,700 |  |
Fair value measured on a recurring basis | Fixed maturity investments. | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 70,500 | 70,000 |  |
Fair value measured on a recurring basis | Short-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 261,700 | 211,300 |  |
Fair value measured on a recurring basis | Short-term investments | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 261,700 | 211,300 |  |
Short-term investments, at amortized cost (which approximates fair value) |  | 211,300 | 453,700 | 376,800
Fair value measured on a recurring basis | Short-term investments | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Short-term investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 73,100 | 70,000 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 73,100 | 70,000 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments |  | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 30,000 | 26,600 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 30,000 | 26,600 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Financials |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 12,900 | 694,700 |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 12,900 | 694,700 |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Communications [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 34,900 | 43,700 |  |
Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 34,900 | 43,700 |  |
Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 39,000 | 35,700 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 39,000 | 35,700 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Technology |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 47,800 | 27,000 |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 47,800 | 27,000 |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 130,500 | 141,800 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 109,000 | 120,500 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 21,500 | 21,300 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Other: |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 74,800 | 74,400 |  |
Fair value measured on a recurring basis | Common equity securities | Other: | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Other: | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 74,800 | 74,400 |  |
Fair value measured on a recurring basis | Common equity securities | Other: | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 443,000 | 1,113,900 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 346,700 | 1,018,200 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 96,300 | 95,700 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Other long-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 172,700 | 169,500 |  |
Fair value measured on a recurring basis | Other long-term investments | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Other long-term investments | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0 | 0 |  |
Fair value measured on a recurring basis | Other long-term investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 172,700 | 169,500 |  |
Carrying value of investment accounted for using the equity method | 3,700 | 3,800 | 3,800 | 5,200
Affordable Housing Development Fund [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Other Investments | 14,100 | 14,700 | $ 16,200 | $ 16,800
Affordable Housing Development Fund [Member] | Fair value measured on a recurring basis | Other long-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Other Investments | $ 14,100 | $ 14,700 |  |

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