Basis of Financial Reporting Text Block (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption					$ 12,107,000
Insurance Commissions	$ 362,014,000	$ 1,033,589,000
Profit-Sharing Contingent Commission Revenue	(14,327,000)	(39,993,000)
Fees and Commissions, Other	138,664,000	375,918,000
Operating Leases, Future Minimum Payments Due	209,800,000	209,800,000			210,400,000
Share-based Compensation		23,522,000	$ 22,362,000
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Insurance Commissions		26,600,000
Profit-Sharing Contingent Commission Revenue		6,900,000
Fees and Commissions, Other		(5,000,000.0)
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption				$ 117,500,000	$ 117,515,000
Cost to Obtain [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Costs	$ 10,300,000	10,300,000
Capitalized Contract Cost, Amortization		300,000
Cost to Fulfill [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Costs				$ 52,700,000
Capitalized Contract Cost, Amortization		$ 3,600,000