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Fair Value Measurement (Assets and Liabilities Measured at Fair Value) (Details) - USD ($) $ in Thousands | Mar. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Assets: |  |
Equity securities | $ 391,206 | $ 387,274
Other investments | 80,576 | 81,892
LP/LLC interests carried at NAV which approximates fair value. These interests, reported as a part of Investment in unconsolidated subsidiaries, are not categorized within the fair value hierarchy. | 199,696 | 204,719
Level 3 [Member] | Corporate debt with limited observable inputs [Member] |  |
Assets: |  |
Total assets categorized within the fair value hierarchy | 18,914 | 14,810
Level 3 [Member] | Other asset-backed securities [Member] |  |
Assets: |  |
Total assets categorized within the fair value hierarchy | 3,002 | 3,007
Fair Value, Measurements, Recurring [Member] |  |
Assets: |  |
Other investments | 29,978 | 31,501
Total assets categorized within the fair value hierarchy | 3,305,954 | 3,474,265
LP/LLC interests carried at NAV which approximates fair value. These interests, reported as a part of Investment in unconsolidated subsidiaries, are not categorized within the fair value hierarchy. | 199,696 | 204,719
Total assets at fair value, including NAV value not within fair value hierarchy | 3,505,650 | 3,678,984
Fair Value, Measurements, Recurring [Member] | U.S. Treasury obligations [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 148,211 | 146,539
Fair Value, Measurements, Recurring [Member] | U.S. Government-sponsored enterprise obligations [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 28,701 | 30,235
Fair Value, Measurements, Recurring [Member] | State and municipal bonds [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 770,061 | 800,463
Fair Value, Measurements, Recurring [Member] | Corporate debt, multiple observable inputs [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 1,287,059 | 1,264,181
Fair Value, Measurements, Recurring [Member] | Corporate debt with limited observable inputs [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 18,914 | 14,810
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 207,906 | 217,906
Fair Value, Measurements, Recurring [Member] | Agency commercial mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 12,688 | 12,783
Fair Value, Measurements, Recurring [Member] | Other commercial mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 19,697 | 19,611
Fair Value, Measurements, Recurring [Member] | Other asset-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 111,192 | 106,878
Fair Value, Measurements, Recurring [Member] | Financial [Member] |  |
Assets: |  |
Equity securities | 84,052 | 81,749
Fair Value, Measurements, Recurring [Member] | Utilities/Energy [Member] |  |
Assets: |  |
Equity securities | 51,304 | 52,869
Fair Value, Measurements, Recurring [Member] | Consumer oriented [Member] |  |
Assets: |  |
Equity securities | 60,686 | 61,284
Fair Value, Measurements, Recurring [Member] | Industrial [Member] |  |
Assets: |  |
Equity securities | 52,497 | 54,265
Fair Value, Measurements, Recurring [Member] | Bond funds [Member] |  |
Assets: |  |
Equity securities | 92,753 | 90,002
Fair Value, Measurements, Recurring [Member] | All other [Member] |  |
Assets: |  |
Equity securities | 49,914 | 47,105
Fair Value, Measurements, Recurring [Member] | Short-term investments [Member] |  |
Assets: |  |
Short-term investments | 280,341 | 442,084
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] |  |
Assets: |  |
Other investments | 1,270 | 1,956
Total assets categorized within the fair value hierarchy | 672,365 | 799,066
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. Treasury obligations [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. Government-sponsored enterprise obligations [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | State and municipal bonds [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate debt, multiple observable inputs [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 2,395 | 2,339
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate debt with limited observable inputs [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Residential mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Agency commercial mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Other commercial mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Other asset-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Financial [Member] |  |
Assets: |  |
Equity securities | 84,052 | 81,749
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Utilities/Energy [Member] |  |
Assets: |  |
Equity securities | 51,304 | 52,869
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Consumer oriented [Member] |  |
Assets: |  |
Equity securities | 60,686 | 61,284
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Industrial [Member] |  |
Assets: |  |
Equity securities | 52,497 | 54,265
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Bond funds [Member] |  |
Assets: |  |
Equity securities | 92,753 | 79,843
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | All other [Member] |  |
Assets: |  |
Equity securities | 49,914 | 27,181
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Short-term investments [Member] |  |
Assets: |  |
Short-term investments | 277,494 | 437,580
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] |  |
Assets: |  |
Other investments | 27,805 | 29,542
Total assets categorized within the fair value hierarchy | 2,610,770 | 2,657,379
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Treasury obligations [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 148,211 | 146,539
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Government-sponsored enterprise obligations [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 28,701 | 30,235
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | State and municipal bonds [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 770,061 | 800,463
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate debt, multiple observable inputs [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 1,284,664 | 1,261,842
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate debt with limited observable inputs [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Residential mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 207,906 | 217,906
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency commercial mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 12,688 | 12,783
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Other commercial mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 19,697 | 19,611
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Other asset-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 108,190 | 103,871
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Financial [Member] |  |
Assets: |  |
Equity securities | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Utilities/Energy [Member] |  |
Assets: |  |
Equity securities | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Consumer oriented [Member] |  |
Assets: |  |
Equity securities | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Industrial [Member] |  |
Assets: |  |
Equity securities | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Bond funds [Member] |  |
Assets: |  |
Equity securities | 0 | 10,159
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | All other [Member] |  |
Assets: |  |
Equity securities | 0 | 19,924
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Short-term investments [Member] |  |
Assets: |  |
Short-term investments | 2,847 | 4,504
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] |  |
Assets: |  |
Other investments | 903 | 3
Total assets categorized within the fair value hierarchy | 22,819 | 17,820
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | U.S. Treasury obligations [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | U.S. Government-sponsored enterprise obligations [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | State and municipal bonds [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate debt, multiple observable inputs [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate debt with limited observable inputs [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 18,914 | 14,810
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Residential mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Agency commercial mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Other commercial mortgage-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Other asset-backed securities [Member] |  |
Assets: |  |
Fixed maturities, available for sale | 3,002 | 3,007
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Financial [Member] |  |
Assets: |  |
Equity securities | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Utilities/Energy [Member] |  |
Assets: |  |
Equity securities | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Consumer oriented [Member] |  |
Assets: |  |
Equity securities | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Industrial [Member] |  |
Assets: |  |
Equity securities | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Bond funds [Member] |  |
Assets: |  |
Equity securities | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | All other [Member] |  |
Assets: |  |
Equity securities | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Short-term investments [Member] |  |
Assets: |  |
Short-term investments | $ 0 | $ 0

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