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Fair Value Measurement (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | $ 3,077,373 | $ 2,985,161
Equity securities: | 616,500 | 529,631
Short-term investments: | 367,351 | 253,299
Equity contracts [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liability | 716 | 3
Fair Value, Measurements, Recurring [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 3,077,373 | 2,985,161
Equity securities: | 616,500 | 529,631
Short-term investments: | 367,351 | 253,299
Note receivable | 5,588 | 5,557
Assets, fair value disclosure | 4,066,812 | 3,773,648
Liabilities, fair value | 3,028 | 4,854
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 23,786 | 25,003
Equity securities: | 513,908 | 430,973
Short-term investments: | 347,482 | 236,515
Note receivable | 0 | 0
Assets, fair value disclosure | 885,176 | 692,491
Liabilities, fair value | 716 | 3
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 3,053,587 | 2,960,158
Equity securities: | 33,739 | 31,433
Short-term investments: | 19,869 | 16,784
Note receivable | 5,588 | 5,557
Assets, fair value disclosure | 3,112,783 | 3,013,932
Liabilities, fair value | 2,312 | 4,851
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Equity securities: | 1,213 | 1,445
Short-term investments: | 0 | 0
Note receivable | 0 | 0
Assets, fair value disclosure | 1,213 | 1,445
Liabilities, fair value | 0 | 0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 23,786 | 25,003
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 23,786 | 25,003
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 2,695,108 | 2,620,132
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 2,695,108 | 2,620,132
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 28,438 | 30,952
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 28,438 | 30,952
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 118,024 | 105,524
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 118,024 | 105,524
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 172,963 | 165,789
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 172,963 | 165,789
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 39,054 | 37,761
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 39,054 | 37,761
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed maturity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 513,908 | 430,973
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 513,908 | 430,973
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 33,739 | 31,433
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 33,739 | 31,433
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 1,213 | 1,445
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 1,213 | 1,445
Fair Value, Measurements, Recurring [Member] | Private Equity Funds Net Asset Value [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Equity securities: | 67,640 | 65,780
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Short-term investments: | 52,670 | 48,256
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Short-term investments: | 32,801 | 31,472
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Short-term investments: | 19,869 | 16,784
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Short-term investments: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Short-term investments: | 314,681 | 205,043
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Short-term investments: | 314,681 | 205,043
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Short-term investments: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Short-term investments: | 0 | 0
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liability | 2,312 | 4,851
Liabilities, fair value | 2,312 | 4,851
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liability | 0 | 0
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liability | 2,312 | 4,851
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liability | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Short-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liability | 716 | 3
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liability | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Derivative liability | $ 0 | $ 0

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- Definition Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 35 -Paragraph 54B -URI http://asc.fasb.org/extlink&oid=99392525&loc=SL7495116-110257 + Details
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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Definition Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313 + Details
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- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities. + References No definition available. + Details
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- Definition Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(4)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(5)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(1)(g)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(2)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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