Revenues (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Document Period End Date			Jun. 30, 2019
Investment Income, Nonoperating	$ 1,525,000	$ 731,000	$ 2,606,000	$ 1,332,000
Other Income	762,000	388,000	1,498,000	910,000
Revenues	575,219,000	473,187,000	1,194,499,000	$ 974,648,000
Contract with Customer, Asset and Liability [Table Text Block]	285,099,000		285,099,000		$ 265,994,000
Contract with Customer, Liability	41,700,000		41,700,000		37,000,000.0
Contract with Customer, Liability, Noncurrent	17,000,000		17,000,000		16,500,000
Contract with Customer, Liability	58,726,000		58,726,000		53,496,000
Deferred Revenue, Revenue Recognized	12,800,000
Deferred Costs	19,700,000		19,700,000		13,200,000
Operating Segments [Member]
Segment Reporting Information [Line Items]
Investment Income, Nonoperating	1,051,000		1,728,000
Other Income	0		0
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Investment Income, Nonoperating	1,051,000	482,000
Revenues	696,000	(5,000)	1,184,000
Retail [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Investment Income, Nonoperating	17,000	0	17,000
Other Income	544,000		1,136,000
Revenues	310,738,000	233,317,000	699,969,000
National Programs [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Investment Income, Nonoperating	380,000	132,000	696,000
Other Income	13,000		50,000
Revenues	131,817,000	118,440,000	241,377,000
Wholesale Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Investment Income, Nonoperating	43,000	81,000	83,000
Other Income	205,000		312,000
Revenues	81,171,000	75,568,000	151,680,000
Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Investment Income, Nonoperating	34,000	36,000	82,000
Other Income	0		0
Revenues	50,797,000	$ 45,867,000	100,289,000
Core Commission Revenue [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	369,592,000		788,131,000
Core Commission Revenue [Member] | Retail [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	219,421,000		506,621,000
Core Commission Revenue [Member] | National Programs [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	85,093,000		162,271,000
Core Commission Revenue [Member] | Wholesale Brokerage [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	65,052,000		119,225,000
Core Commission Revenue [Member] | Services [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	0		0
Core Commission Revenue [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	26,000		14,000
Fee Revenue [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	167,715,000		303,504,000
Fee Revenue [Member] | Retail [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	68,827,000		112,704,000
Fee Revenue [Member] | National Programs [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	34,472,000		64,718,000
Fee Revenue [Member] | Wholesale Brokerage [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	13,940,000		26,450,000
Fee Revenue [Member] | Services [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	50,763,000		100,207,000
Fee Revenue [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	(287,000)		(575,000)
Incentive Commission Revenue [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	10,899,000		55,077,000
Incentive Commission Revenue [Member] | Retail [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	12,714,000		55,489,000
Incentive Commission Revenue [Member] | National Programs [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	(1,846,000)		(927,000)
Incentive Commission Revenue [Member] | Wholesale Brokerage [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	125,000		498,000
Incentive Commission Revenue [Member] | Services [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	0		0
Incentive Commission Revenue [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	(94,000)		17,000
Profit-Sharing Contingent Commission Revenue [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	11,983,000		27,305,000
Profit-Sharing Contingent Commission Revenue [Member] | Retail [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	6,659,000		18,206,000
Profit-Sharing Contingent Commission Revenue [Member] | National Programs [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	4,093,000		4,953,000
Profit-Sharing Contingent Commission Revenue [Member] | Wholesale Brokerage [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	1,231,000		4,146,000
Profit-Sharing Contingent Commission Revenue [Member] | Services [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	0		0
Profit-Sharing Contingent Commission Revenue [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	0		0
Guaranteed Supplemental Commission Revenue [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	12,743,000		16,378,000
Guaranteed Supplemental Commission Revenue [Member] | Retail [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	2,556,000		5,796,000
Guaranteed Supplemental Commission Revenue [Member] | National Programs [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	9,612,000		9,616,000
Guaranteed Supplemental Commission Revenue [Member] | Wholesale Brokerage [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	575,000		966,000
Guaranteed Supplemental Commission Revenue [Member] | Services [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	0		0
Guaranteed Supplemental Commission Revenue [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Fees and Commissions, Other	0		0
Cost to Obtain [Member]
Segment Reporting Information [Line Items]
Deferred Costs	7,100,000		7,100,000
Capitalized Contract Cost, Amortization			600,000
Cost to Fulfill [Member]
Segment Reporting Information [Line Items]
Deferred Costs	$ 69,000,000.0		69,000,000.0		$ 69,800,000
Capitalized Contract Cost, Amortization			$ 800,000