Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Dec. 31, 2014
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount	$ 1,600,000
Operating Loss Carryforwards State	42,500,000
Operating Loss Carryforwards	100,000
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	(644,000)	$ (126,000)	$ (205,000)
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(5,000)	0	(41,000)
Deferred Tax Assets, Valuation Allowance	(896,000)	(893,000)
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	594,000	1,070,000	412,000
Deferred income taxes, net	315,732,000	256,185,000		$ 300,760,000
Deferred Tax Assets, Operating Loss Carryforwards	2,196,000	2,434,000
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation	41,293,000	36,701,000
Liability for Uncertain Tax Positions, Current	197,205	228,608	86,191
Income Taxes Paid	$ 110,557,000	152,024,000	143,111,000
Document Period End Date	Dec. 31, 2018
Unrecognized Tax Benefits	$ 1,639,000	1,694,000	$ 750,000		$ 584,000
Deferred Tax Liabilities, Property, Plant and Equipment	4,929,000	2,723,000
deferred profit sharing contingent commissions	$ 0	$ 7,107,000
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	21.00%	35.00%	35.00%
Current Federal Tax Expense (Benefit)	$ 77,694,000	$ 129,954,000	$ 126,145,000
Current State and Local Tax Expense (Benefit)	25,096,000	21,392,000	21,110,000
Current Foreign Tax Expense (Benefit)	409,000	929,000	590,000
Deferred Federal Income Tax Expense (Benefit)	8,483,000	18,999,000	15,551,000
Current Income Tax Expense (Benefit)	103,199,000	152,275,000	147,845,000
Deferred State and Local Income Tax Expense (Benefit)	6,519,000	2,984,000	2,612,000
Deferred Foreign Income Tax Expense (Benefit)	6,000	0	0
Summary of Income Tax Contingencies [Table Text Block]	15,008,000	(102,183,000)	18,163,000
Income Tax Expense (Benefit)	$ (118,207,000)	$ (50,092,000)	$ (166,008,000)
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent	5.70%	3.80%	3.90%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Percent	0.20%	0.30%	0.30%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Meals and Entertainment, Percent	0.30%	0.30%	0.30%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount	$ 0.003	$ 0
Tax Reform Act Deferred Tax Revaluation and Transition Tax Impact	(0.30%)	(26.90%)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Percent	(1.60%)	(1.40%)	(0.30%)
Effective Income Tax Rate Reconciliation, Percent	25.60%	11.10%	39.20%
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals	$ 10,455,000	$ 7,534,000
Net Unrealized Holding Gain on Available for Sale Securities	(78,000)	(6,000)
Deferred Tax Liabilities, Goodwill and Intangible Assets	334,200,000	306,351,000
Non Current Deferred Tax Liability	368,780,000	309,068,000
Deferred Tax Assets, Net, Noncurrent	$ 53,048,000	52,883,000
Tax Cuts and Jobs Act 2017 [Member]
Income Tax Contingency [Line Items]
Taxes Payable		3,300,000
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	21.00%
Income Tax Expense (Benefit)		120,900,000
Deferred Tax Liabilities, Deferred Expense	$ 0	$ (124,166,000)
Accounting Standards Update 2014-09 [Member]
Income Tax Contingency [Line Items]
Deferred Tax Liabilities, Other	$ 29,729,000