Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets:
Equity securities	$ 384,519	$ 376,697
Loans receivable	151,920	275,747
Fair Value
Assets:
Fixed maturity securities	12,765,246	12,462,847
Equity securities available for sale	141,699	150,866
Equity securities	384,519	376,697
Loans receivable	151,920	275,747
Cash and cash equivalents	837,515	763,631
Trading account receivables from brokers and clearing organizations	373,833	383,115
Due From Brokers, Fair Value Disclosure	0	1,713
Liabilities:
Trading account securities sold but not yet purchased	35,956	37,035
Subordinated debentures	462,256	355,880
Senior notes and other debt	2,018,282	2,029,572
Carrying Value
Assets:
Fixed maturity securities	12,745,436	12,444,394
Equity securities available for sale	141,699	150,866
Equity securities	384,519	376,697
Loans receivable	149,388	273,103
Cash and cash equivalents	837,515	763,631
Trading account receivables from brokers and clearing organizations	373,833	383,115
Due From Brokers, Fair Value Disclosure	0	1,713
Due from broker fair value	71,024	0
Liabilities:
Trading account securities sold but not yet purchased	35,956	37,035
Subordinated debentures	446,485	340,320
Senior notes and other debt	$ 1,814,998	$ 1,844,621