Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Assets:
Equity securities	$ 351,179	$ 450,648
Loans receivable	289,061	325,219
Fair Value
Assets:
Fixed maturity securities	12,386,845	12,725,806
Equity securities available for sale	177,877	170,991
Equity securities	351,179	450,648
Loans receivable	289,061	325,219
Cash and cash equivalents	879,934	674,441
Trading account receivables from brokers and clearing organizations	401,941	371,034
Liabilities:
Trading account securities sold but not yet purchased	33,360	106,079
Subordinated debentures	343,000	332,640
Senior notes and other debt	2,047,134	2,344,292
Carrying Value
Assets:
Fixed maturity securities	12,368,319	12,705,160
Equity securities available for sale	177,877	170,991
Equity securities	351,179	450,648
Loans receivable	286,273	322,012
Cash and cash equivalents	879,934	674,441
Trading account receivables from brokers and clearing organizations	401,941	371,034
Due from broker fair value	64,343	23,133
Liabilities:
Trading account securities sold but not yet purchased	33,360	106,079
Subordinated debentures	340,255	340,060
Senior notes and other debt	$ 1,838,965	$ 2,115,527