Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Assets:
Equity securities available for sale	$ 602,965	$ 376,697
Loans receivable	116,483	275,747
Fair Value
Assets:
Fixed maturity securities	13,636,291	12,462,847
Equity securities available for sale	158,975	150,866
Equity securities available for sale	602,965	376,697
Loans receivable	116,483	275,747
Cash and cash equivalents	873,064	763,631
Trading account receivables from brokers and clearing organizations	185,548	383,115
Due From Brokers, Fair Value Disclosure	0	1,713
Due from broker fair value	101,405	0
Liabilities:
Trading account securities sold but not yet purchased	60,959	37,035
Subordinated debentures	779,056	355,880
Senior notes and other debt	1,997,430	2,029,572
Carrying Value
Assets:
Fixed maturity securities	13,616,671	12,444,394
Equity securities available for sale	158,975	150,866
Equity securities available for sale	602,965	376,697
Loans receivable	113,996	273,103
Cash and cash equivalents	873,064	763,631
Trading account receivables from brokers and clearing organizations	185,548	383,115
Due From Brokers, Fair Value Disclosure	0	1,713
Due from broker fair value	101,405	0
Liabilities:
Trading account securities sold but not yet purchased	60,959	37,035
Subordinated debentures	727,390	340,320
Senior notes and other debt	$ 1,762,487	$ 1,844,621