Revenues (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Document Period End Date			Sep. 30, 2018
Insurance Commissions	$ 362,014,000		$ 1,033,589,000
Investment Income, Nonoperating	719,000	$ 491,000	2,051,000	$ 1,085,000
Other Income	318,000	546,000	1,228,000	22,047,000
Fees and Commissions, Other	138,664,000		375,918,000
Incentive Commission	11,755,000		44,194,000
Profit-Sharing Contingent Commission Revenue	14,327,000		39,993,000
Guaranteed Supplemental Commission	3,053,000		8,525,000
Revenues	530,850,000	475,646,000	1,505,498,000	1,407,031,000
Contract with Customer, Asset and Liability [Table Text Block]	249,294,000		249,294,000		$ 210,323,000
Contract with Customer, Liability	53,900,000		53,900,000		44,500,000
Contract with Customer, Liability, Noncurrent	9,700,000		9,700,000		6,700,000
Contract with Customer, Liability	63,611,000		63,611,000		$ 51,236,000
Deferred Revenue, Revenue Recognized			8,100,000
Operating Segments [Member]
Segment Reporting Information [Line Items]
Insurance Commissions	(11,000)		(42,000)
Investment Income, Nonoperating	485,000		1,380,000
Other Income	0		9,000
Fees and Commissions, Other	(360,000)		(880,000)
Incentive Commission	16,000		28,000
Profit-Sharing Contingent Commission Revenue	0		0
Guaranteed Supplemental Commission	0		0
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Investment Income, Nonoperating	485,000	292,000	1,380,000	576,000
Revenues	130,000	380,000	495,000	20,507,000
Retail [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Insurance Commissions	207,703,000		609,252,000
Investment Income, Nonoperating	1,000	3,000	2,000	6,000
Other Income	207,000		758,000
Fees and Commissions, Other	33,915,000		94,282,000
Incentive Commission	11,408,000		43,356,000
Profit-Sharing Contingent Commission Revenue	5,280,000		17,879,000
Guaranteed Supplemental Commission	2,573,000		7,277,000
Revenues	261,087,000	234,483,000	772,806,000	712,739,000
National Programs [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Insurance Commissions	92,106,000		249,491,000
Investment Income, Nonoperating	138,000	124,000	384,000	279,000
Other Income	12,000		60,000
Fees and Commissions, Other	43,168,000		106,839,000
Incentive Commission	287,000		295,000
Profit-Sharing Contingent Commission Revenue	7,786,000		17,290,000
Guaranteed Supplemental Commission	22,000		75,000
Revenues	143,519,000	127,718,000	374,434,000	342,576,000
Wholesale Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Insurance Commissions	62,216,000		174,888,000
Investment Income, Nonoperating	44,000	0	125,000	0
Other Income	99,000		401,000
Fees and Commissions, Other	13,887,000		37,799,000
Incentive Commission	44,000		515,000
Profit-Sharing Contingent Commission Revenue	1,261,000		4,824,000
Guaranteed Supplemental Commission	458,000		1,173,000
Revenues	78,009,000	71,574,000	219,725,000	208,812,000
Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Insurance Commissions	0		0
Investment Income, Nonoperating	51,000	72,000	160,000	224,000
Other Income	0		0
Fees and Commissions, Other	48,054,000		137,878,000
Incentive Commission	0		0
Profit-Sharing Contingent Commission Revenue	0		0
Guaranteed Supplemental Commission	0		0
Revenues	$ 48,105,000	$ 41,491,000	$ 138,038,000	$ 122,397,000