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Reserve for Loss and Loss Expense (Roll Forward of Gross and Net Asbestos and Net Environmental Incurred Losses and Loss Expenses and Related Reserves) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |
Salvage and Subrogation Recoveries, Value | $ 64,800 | $ 64,900 | $ 62,100
Reserve for loss and loss expense at beginning of year, gross | 29,962 | 30,411 | 30,653
Incurred loss and loss expense, gross | 126 | 1,483 | 2,968
Less: loss and loss expense paid, gross | (1,673) | (1,932) | (3,210)
Reserve for loss and loss expense at the end of year, gross | 28,415 | 29,962 | 30,411
Reserve for loss and loss expense at beginning of year, net | 22,716 | 23,161 | 22,994
Incurred loss and loss expense, net | 0 | 1,380 | 3,320
Less: loss and loss expense paid, net | (1,504) | (1,825) | (3,153)
Reserve for loss and loss expense at the end of year, net | 21,212 | 22,716 | 23,161
Asbestos [Member] |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |
Reserve for loss and loss expense at beginning of year, gross | 7,847 | 8,024 | 8,751
Incurred loss and loss expense, gross | 0 | 77 | 428
Less: loss and loss expense paid, gross | (270) | (254) | (299)
Reserve for loss and loss expense at the end of year, gross | 7,577 | 7,847 | 8,024
Reserve for loss and loss expense at beginning of year, net | 6,615 | 6,793 | 7,314
Incurred loss and loss expense, net | 0 | 77 | (77)
Less: loss and loss expense paid, net | (269) | (255) | (444)
Reserve for loss and loss expense at the end of year, net | 6,346 | 6,615 | 6,793
Enviromental [Member] |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |
Reserve for loss and loss expense at beginning of year, gross | 22,115 | 22,387 | 21,902
Incurred loss and loss expense, gross | 126 | 1,406 | 3,396
Less: loss and loss expense paid, gross | (1,403) | (1,678) | (2,911)
Reserve for loss and loss expense at the end of year, gross | 20,838 | 22,115 | 22,387
Reserve for loss and loss expense at beginning of year, net | 16,101 | 16,368 | 15,680
Incurred loss and loss expense, net | 0 | 1,303 | 3,397
Less: loss and loss expense paid, net | (1,235) | (1,570) | (2,709)
Reserve for loss and loss expense at the end of year, net | $ 14,866 | $ 16,101 | $ 16,368

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- Definition Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to asbestos and environmental claims, before estimated recoveries from reinsurers. + 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 (a) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 + Details
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- Definition Amount, before effects of reinsurance, of expense for claims incurred and costs incurred in the claim settlement process attributable to asbestos and environmental claims. + 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 (b) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 + Details
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- Definition Amount of cash outflow to settle insured claims and pay costs incurred in the claims settlement process attributable to asbestos and environmental claims. + 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=65670824&loc=d3e14764-158437 + Details
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- Definition Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to asbestos and environmental claims, net of estimated reinsurance recoveries. + 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 (cc) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 + Details
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- Definition Amount, after effects of reinsurance, of expense for claims incurred and costs incurred in the claim settlement process attributable to asbestos and environmental claims. + 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 (b) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 + Details
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- Definition Amount, after effects of reinsurance, of payments to settle insured claims and pay costs incurred in the claims settlement process attributable to asbestos and environmental claims. + 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=65670824&loc=d3e14764-158437 + Details
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- Definition The estimated amount as of the balance sheet date to be received by an insurer from the sale of property (usually damaged) on which the insurer has paid a total claim to the insured and has obtained title to the property and the right of an insurer to pursue any course of recovery of damages, in its name or in the name of the policyholder, against a third party who is liable for costs relating to an insured event that have been paid by the insurer. Estimated salvage and subrogation is generally deducted from the liability for unpaid claims. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 30 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6482241&loc=d3e13779-158432 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 30 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6482241&loc=d3e13783-158432 + Details
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