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Reserve for Losses and Loss Expenses (Reserve Loss Development) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years | $ 641,174 | $ 592,062 | $ 572,434
Favorable or adverse loss development | (69,009) | (59,269) | (25,525)
Property Development |  |  | 11,000
Favorable or unfavorable loss development [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years | 69,000 | 59,300 | 25,500
Favorable or adverse loss development | (69,000) | (59,300) | (25,500)
Property Development | 2,000 | 11,100 |
Casualty Development | 67,000 | 48,200 | 14,500
Favorable or unfavorable loss development [Member] | General Liability [Member] |  |  |
Favorable or adverse loss development | (51,000) | (43,900) | (20,000)
Favorable or unfavorable loss development [Member] | Commercial Automobile [Member] |  |  |
Favorable or adverse loss development | 2,400 | (4,100) | (4,500)
Favorable or unfavorable loss development [Member] | Workers' Compensation [Member] |  |  |
Favorable or adverse loss development | (37,000) | 0 | 23,500
Favorable or unfavorable loss development [Member] | Business Owners' Policies [Member] |  |  |
Favorable or adverse loss development | 2,200 | 1,900 | (9,500)
Favorable or unfavorable loss development [Member] | Commercial Property [Member] |  |  |
Favorable or adverse loss development | (3,000) | (2,100) | (7,500)
Favorable or unfavorable loss development [Member] | Homeowners [Member] |  |  |
Favorable or adverse loss development | 1,500 | (4,000) | (2,500)
Favorable or unfavorable loss development [Member] | Personal Automobile [Member] |  |  |
Favorable or adverse loss development | 400 | (10,800) | (3,000)
Favorable or unfavorable loss development [Member] | Excess And Surplus Operations [Member] |  |  |
Favorable or adverse loss development | $ 15,500 | $ 3,700 | $ (2,000)

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- Definition Amount of provision in the period for casualty claims incurred in prior reporting periods and related claims settlement costs. + References No definition available. + Details
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- Definition Amount of provision in the period for property claims incurred in prior reporting periods and related claims settlement. + References No definition available. + Details
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- Definition Amount of payments to settle claims incurred in prior periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 + Details
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- Definition Amount of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-18) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915 + Details
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