Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Liability for Uncertain Tax Positions, Current	$ 102,171	$ 65,772
Income Taxes Paid	132,874,000	118,290,000	$ 110,190,000
Unrecognized Tax Benefits	583,977	113,032	$ 391,000	$ 294,000
Deferred Tax Liabilities, Property, Plant and Equipment	8,585,000	10,368,000
deferred profit sharing contingent commissions	$ 9,767,000	$ 10,335,000
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	35.00%	35.00%	35.00%
Current Federal Tax Expense (Benefit)	$ 118,490,000	$ 109,893,000	$ 94,007,000
Current State and Local Tax Expense (Benefit)	17,625,000	15,482,000	13,438,000
Current Foreign Tax Expense (Benefit)	430,000	109,000	805,000
Current Income Tax Expense (Benefit)	136,545,000	125,484,000	108,250,000
Deferred Federal Income Tax Expense (Benefit)	18,416,000	5,987,000	28,469,000
Deferred State and Local Income Tax Expense (Benefit)	4,280,000	1,440,000	3,723,000
Deferred Foreign Income Tax Expense (Benefit)	0	(58,000)	55,000
Summary of Income Tax Contingencies [Table Text Block]	22,696,000	7,369,000	32,247,000
Income Tax Expense (Benefit)	$ 159,241,000	$ 132,853,000	$ 140,497,000
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent	3.90%	3.30%	3.50%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Percent	0.30%	0.30%	0.30%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Meals and Entertainment, Percent	0.30%	0.40%	0.30%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Percent	0.10%	0.10%	0.20%
Effective Income Tax Rate Reconciliation, Percent	39.60%	39.10%	39.30%
Deferred Tax Assets Operating Loss Carryforwards Current	$ 10,000	$ 951,000
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals	14,858,000	14,145,000
Deferred Tax Assets, Net, Current	24,635,000	25,431,000
Net Unrealized Holding Gain on Available for Sale Securities	(9,000)	56,000
Deferred Tax Liabilities, Goodwill and Intangible Assets	393,251,000	364,938,000
Non Current Deferred Tax Liability	401,827,000	375,362,000
Deferred income taxes, net	360,949,000	341,497,000
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation	38,966,000	31,580,000
Deferred Tax Assets, Operating Loss Carryforwards	2,518,000	2,796,000
Deferred Tax Assets, Valuation Allowance	(606,000)	(511,000)
Deferred Tax Assets, Net, Noncurrent	40,878,000	33,865,000
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	773,000	0	$ 232,000
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	0	(21,000)	0
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	(302,000)	$ (257,000)	$ (135,000)
Operating Loss Carryforwards	184,218
Operating Loss Carryforwards State	$ 61,217,003
Operating Loss Carryforwards, Expiration Date	2034