Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets:
Arbitrage trading account	$ 450,648us-gaap_TradingSecurities	$ 522,128us-gaap_TradingSecurities
Loans receivable	325,219	346,746
Due To Broker	23,133wrb_DueToBroker	8,273wrb_DueToBroker
Due To Broker Fair Value	23,133wrb_DueToBrokerFairValue	8,273wrb_DueToBrokerFairValue
Carrying Value
Assets:
Fixed maturity securities	12,705,160	11,616,844
Equity securities available for sale	170,991	283,338
Arbitrage trading account	450,648	522,128
Loans receivable	322,012	343,583
Cash and cash equivalents	674,441	839,738
Trading accounts receivable from brokers and clearing organizations	371,034	304,936
Due from broker	0	17,735
Liabilities:
Trading account securities sold but not yet purchased	106,079	162,278
Subordinated debentures	340,060	339,800
Senior notes and other debt	2,115,527	1,692,442
Fair Value
Assets:
Fixed maturity securities	12,725,806	11,631,744
Equity securities available for sale	170,991	283,338
Arbitrage trading account	450,648	522,128
Loans receivable	325,219	346,746
Cash and cash equivalents	674,441	839,738
Trading accounts receivable from brokers and clearing organizations	371,034	304,936
Due from broker	0	17,735
Liabilities:
Trading account securities sold but not yet purchased	106,079	162,278
Subordinated debentures	332,640	288,540
Senior notes and other debt	$ 2,344,292	$ 1,861,898

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Fair value portion of liabilities pertaining to principal and customer trading transactions, or which may be incurred with the objective of generating a profit from short-term fluctuations in price as part of an entity's market-making, hedging and proprietary trading. Examples include, but are not limited to, short positions in securities, derivatives and commodities.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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Due From Brokers, Fair Value Disclosure

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Due to broker.

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Due To Broker Fair Value

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Marketable Securities, Fair Value Disclosure

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Trading Accounts Receivable From Brokers, Fair Value Disclosure

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