Revenues (Details) - USD ($) | 3 Months Ended | |
Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2018 |
Segment Reporting Information [Line Items] | | | |
Document Period End Date | Mar. 31, 2019 | | |
Investment Income, Nonoperating | $ 1,081,000 | $ 601,000 | |
Other Income | 736,000 | 522,000 | |
Revenues | 619,280,000 | 501,461,000 | |
Contract with Customer, Asset and Liability [Table Text Block] | 311,137,000 | | $ 265,994,000 |
Contract with Customer, Liability | 39,600,000 | | 37,000,000 |
Contract with Customer, Liability, Noncurrent | 17,700,000 | | 16,500,000 |
Contract with Customer, Liability | $ 57,283,000 | | 53,496,000 |
Deferred Revenue, Revenue Recognized | not significant | | |
Deferred Costs | $ 16,300,000 | | 13,200,000 |
Operating Segments [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Investment Income, Nonoperating | 677,000 | | |
Other Income | 0 | | |
Segment Reconciling Items [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Investment Income, Nonoperating | 677,000 | 413,000 | |
Revenues | 488,000 | 370,000 | |
Retail [Member] | Operating Segments [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Investment Income, Nonoperating | 0 | 1,000 | |
Other Income | 592,000 | | |
Revenues | 389,231,000 | 278,402,000 | |
National Programs [Member] | Operating Segments [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Investment Income, Nonoperating | 316,000 | 114,000 | |
Other Income | 37,000 | | |
Revenues | 109,560,000 | 112,475,000 | |
Wholesale Brokerage [Member] | Operating Segments [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Investment Income, Nonoperating | 40,000 | 0 | |
Other Income | 107,000 | | |
Revenues | 70,509,000 | 66,148,000 | |
Services [Member] | Operating Segments [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Investment Income, Nonoperating | 48,000 | 73,000 | |
Other Income | 0 | | |
Revenues | 49,492,000 | $ 44,066,000 | |
Core Commission Revenue [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 418,539,000 | | |
Core Commission Revenue [Member] | Retail [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 287,200,000 | | |
Core Commission Revenue [Member] | National Programs [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 77,178,000 | | |
Core Commission Revenue [Member] | Wholesale Brokerage [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 54,173,000 | | |
Core Commission Revenue [Member] | Services [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 0 | | |
Core Commission Revenue [Member] | Other Segments [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | (12,000) | | |
Fee Revenue [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 135,789,000 | | |
Fee Revenue [Member] | Retail [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 43,877,000 | | |
Fee Revenue [Member] | National Programs [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 30,246,000 | | |
Fee Revenue [Member] | Wholesale Brokerage [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 12,510,000 | | |
Fee Revenue [Member] | Services [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 49,444,000 | | |
Fee Revenue [Member] | Other Segments [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | (288,000) | | |
Incentive Commission Revenue [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 44,178,000 | | |
Incentive Commission Revenue [Member] | Retail [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 42,775,000 | | |
Incentive Commission Revenue [Member] | National Programs [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 919,000 | | |
Incentive Commission Revenue [Member] | Wholesale Brokerage [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 373,000 | | |
Incentive Commission Revenue [Member] | Services [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 0 | | |
Incentive Commission Revenue [Member] | Other Segments [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 111,000 | | |
Profit-Sharing Contingent Commission Revenue [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 15,322,000 | | |
Profit-Sharing Contingent Commission Revenue [Member] | Retail [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 11,547,000 | | |
Profit-Sharing Contingent Commission Revenue [Member] | National Programs [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 860,000 | | |
Profit-Sharing Contingent Commission Revenue [Member] | Wholesale Brokerage [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 2,915,000 | | |
Profit-Sharing Contingent Commission Revenue [Member] | Services [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 0 | | |
Profit-Sharing Contingent Commission Revenue [Member] | Other Segments [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 0 | | |
Guaranteed Supplemental Commission Revenue [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 3,635,000 | | |
Guaranteed Supplemental Commission Revenue [Member] | Retail [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 3,240,000 | | |
Guaranteed Supplemental Commission Revenue [Member] | National Programs [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 4,000 | | |
Guaranteed Supplemental Commission Revenue [Member] | Wholesale Brokerage [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 391,000 | | |
Guaranteed Supplemental Commission Revenue [Member] | Services [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 0 | | |
Guaranteed Supplemental Commission Revenue [Member] | Other Segments [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Fees and Commissions, Other | 0 | | |
Cost to Obtain [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Deferred Costs | 3,400,000 | | |
Capitalized Contract Cost, Amortization | 300,000 | | |
Cost to Fulfill [Member] | | | |
Segment Reporting Information [Line Items] | | | |
Deferred Costs | 62,400,000 | | $ 69,800,000 |
Capitalized Contract Cost, Amortization | $ 7,400,000 | | |