Basis of Financial Reporting Adopted Guidance (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Premiums Commissions And Fees Receivable	$ 694,266		$ 699,460	$ 546,402
Other Assets, Current	92,898		100,544	47,864
Insurance Commissions and Fees	500,338	$ 444,566
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	27,410
Retained Earnings (Accumulated Deficit)	2,644,191		2,574,114	2,456,599
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				12,107
Premiums Payable To Insurance Companies	695,964		697,270	685,163
Accounts Payable, Current	125,034		72,924	64,177
Accrued Liabilities, Current	157,028		251,542	228,748
Deferred Tax Liabilities, Net, Noncurrent	288,653		$ 300,760	256,185
Employee Compensation And Benefits	270,899	245,866
Other Cost and Expense, Operating	76,313	66,919
Income Tax Expense (Benefit)	27,613	40,857
Net Income (Loss) Attributable to Parent	90,828	$ 70,110
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	11,141
Accounts Payable [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				8,747
Other Liabilities [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				22,794
Deferred Income Tax Charge [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				44,575
Employee Compensation and Benefits [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	10,121
Operating Expense [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	2,761
Income Tax Expense [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	3,387
Retained Earnings [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				117,515
Premiums Receivable [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				153,058
Other Current Assets [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				$ 52,680
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Insurance Commissions and Fees	472,928
Employee Compensation And Benefits	260,778
Other Cost and Expense, Operating	73,552
Income Tax Expense (Benefit)	24,226
Net Income (Loss) Attributable to Parent	$ 79,687