Revenues (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Document Period End Date			Jun. 30, 2018
Insurance Commissions	$ 333,583,000		$ 671,578,000
Investment Income, Nonoperating	731,000	$ 351,000	1,332,000	$ 594,000
Other Income	388,000	1,230,000	910,000	21,501,000
Fees and Commissions, Other	113,388,000		237,251,000
Incentive Commission	8,623,000		32,439,000
Profit-Sharing Contingent Commission Revenue	13,981,000		25,665,000
Guaranteed Supplemental Commission	2,493,000		5,473,000
Revenues	473,187,000	466,305,000	974,648,000	931,385,000
Contract with Customer, Asset and Liability [Table Text Block]	213,477,000		213,477,000		$ 210,323,000
Contract with Customer, Liability	50,500,000		50,500,000		44,500,000
Contract with Customer, Liability, Noncurrent	8,900,000		8,900,000		6,700,000
Contract with Customer, Liability	59,361,000		59,361,000		$ 51,236,000
Operating Segments [Member]
Segment Reporting Information [Line Items]
Insurance Commissions	(155,000)		(29,000)
Investment Income, Nonoperating	482,000		895,000
Other Income	(49,000)		9,000
Fees and Commissions, Other	(286,000)		(522,000)
Incentive Commission	3,000		12,000
Profit-Sharing Contingent Commission Revenue	0		0
Guaranteed Supplemental Commission	0		0
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Investment Income, Nonoperating	482,000	197,000	895,000	284,000
Revenues	(5,000)	90,000	365,000	20,127,000
Retail [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Insurance Commissions	193,242,000		401,548,000
Investment Income, Nonoperating	0	1,000	1,000	3,000
Other Income	346,000		551,000
Fees and Commissions, Other	22,689,000		60,367,000
Incentive Commission	8,389,000		31,949,000
Profit-Sharing Contingent Commission Revenue	6,469,000		12,599,000
Guaranteed Supplemental Commission	2,182,000		4,704,000
Revenues	233,317,000	238,969,000	511,719,000	478,256,000
National Programs [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Insurance Commissions	80,281,000		157,383,000
Investment Income, Nonoperating	132,000	81,000	246,000	155,000
Other Income	19,000		48,000
Fees and Commissions, Other	32,479,000		63,672,000
Incentive Commission	(31,000)		9,000
Profit-Sharing Contingent Commission Revenue	5,521,000		9,503,000
Guaranteed Supplemental Commission	39,000		54,000
Revenues	118,440,000	113,675,000	230,915,000	214,858,000
Wholesale Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Insurance Commissions	60,215,000		112,676,000
Investment Income, Nonoperating	81,000	0	81,000	0
Other Income	72,000		302,000
Fees and Commissions, Other	12,675,000		23,910,000
Incentive Commission	262,000		469,000
Profit-Sharing Contingent Commission Revenue	1,991,000		3,563,000
Guaranteed Supplemental Commission	272,000		715,000
Revenues	75,568,000	71,991,000	141,716,000	137,238,000
Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Insurance Commissions	0		0
Investment Income, Nonoperating	36,000	72,000	109,000	152,000
Other Income	0		0
Fees and Commissions, Other	45,831,000		89,824,000
Incentive Commission	0		0
Profit-Sharing Contingent Commission Revenue	0		0
Guaranteed Supplemental Commission	0		0
Revenues	$ 45,867,000	$ 41,580,000	$ 89,933,000	$ 80,906,000