Basis of Financial Reporting Adopted Guidance (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Premiums Commissions And Fees Receivable	$ 736,378		$ 736,378		$ 699,460	$ 546,402
Other Assets, Current	95,799		95,799		100,544	47,864
Insurance Commissions and Fees	529,813	$ 474,609	1,502,219	$ 1,383,899
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			(24,700)
Retained Earnings (Accumulated Deficit)	2,782,504		2,782,504		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	732,550		732,550		697,270	685,163
Accounts Payable, Current	84,228		84,228		72,924	64,177
Accrued Liabilities, Current	234,731		234,731		251,542	228,748
Deferred Tax Liabilities, Net, Noncurrent	284,330		284,330		300,760	256,185
Employee Compensation And Benefits	268,045	246,062	790,902	736,445
Other Cost and Expense, Operating	83,697	72,058	243,704	210,289
Income Tax Expense (Benefit)	36,447	48,506	91,048	131,263
Net Income (Loss) Attributable to Parent	106,053	$ 75,913	270,803	$ 212,125
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income			15,791
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			3,396
Operating Expense [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			(6,996)
Income Tax Expense [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			$ 5,309
Retained Earnings [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification					$ 117,500	117,515
Other Current Assets [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification						52,680
Premiums Receivable [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification						$ 153,058
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Insurance Commissions and Fees	1,477,519
Employee Compensation And Benefits	794,298
Other Cost and Expense, Operating	236,708
Income Tax Expense (Benefit)	85,739
Net Income (Loss) Attributable to Parent	$ 255,012