Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Assets
Fixed maturity securities	$ 11,312,037	$ 11,209,154
Fixed maturity securities, fair value	11,330,910	11,215,317
Equity securities available for sale	443,439	561,053
Equity securities available for sale, fair value	443,439	561,053
Arbitrage trading account	397,312	359,192
Arbitrage trading account, fair value	397,312	359,192
Loans receivable	263,187	353,583
Loans receivable, fair value	245,169	312,515
Cash and cash equivalents	911,742	642,952	515,430	1,134,835
Cash and cash equivalents, fair value	911,742	642,952
Trading account receivable from brokers and clearing organizations	318,240	339,235
Trading account receivables from brokers and clearing organizations, fair value	318,240	339,235
Due from broker	10,875	0
Due from broker fair value	10,875	0
Liabilities
Trading account securities sold but not yet purchased	62,514	53,494
Trading account securities sold but not yet purchased, fair value	62,514	53,494
Junior subordinated debentures	242,997	242,784
Junior subordinated debentures, fair value	258,400	249,900
Senior notes and other debt	1,500,503	1,500,419
Senior notes and other debt, fair value	$ 1,587,473	$ 1,570,057

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