Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Enactment of US Tax Reform		$ 2,500,000
Deferred tax liabilities
Prepaid assets	$ (3,306,000)	(3,957,000)
Depreciation	(3,918,000)	(2,021,000)
Intangibles	(474,000)	0
Software development costs	(4,950,000)	(3,732,000)
Total deferred tax liabilities	(12,648,000)	(9,710,000)
Deferred tax assets
Accrued incentive compensation	8,612,000	3,510,000
Net operating loss carryforward	709,000	774,000
Workers’ compensation accruals	4,739,000	4,586,000
Accrued rent	918,000	676,000
Stock-based compensation	6,183,000	4,233,000
Minority investment impairment	676,000	667,000
Other	305,000	216,000
Total deferred tax assets	22,142,000	14,662,000
Valuation allowance	(678,000)	(669,000)
Total net deferred tax assets	21,464,000	13,993,000
Net deferred tax assets	8,816,000	4,283,000
Current income tax expense
Federal	40,347,000	30,009,000	$ 31,045,000
State	11,133,000	5,988,000	5,190,000
Total current income tax expense	51,480,000	35,997,000	36,235,000
Deferred income tax (benefit) expense
Federal	(3,398,000)	9,549,000	2,641,000
State	(1,135,000)	193,000	310,000
Total deferred income tax (benefit) expense	(4,533,000)	9,742,000	2,951,000
Total income tax expense	46,947,000	45,739,000	39,186,000
Income tax benefit recognized related to Equity Compensation after adoption of ASU 2016-09, Quantification	$ 2,700,000	$ 6,800,000	$ 1,500,000
Reconciliation of income tax expense [Abstract]
Assumed income tax rate (in hundredths)	21.00%	35.00%	35.00%
Expected income tax expense at 21%, 35% and 35%, respectively	$ 38,296,000	$ 45,549,000	$ 36,812,000
State income taxes, net of federal benefit	7,660,000	4,085,000	3,684,000
Nondeductible expenses	4,831,000	2,649,000	1,669,000
Section 199 benefits	0	(875,000)	(686,000)
Equity compensation	(2,737,000)	(6,218,000)	(1,338,000)
Research and development credit	(856,000)	(634,000)	(751,000)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount	0	(669,000)	0
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	0	2,559,000	0
Other, net	(247,000)	(707,000)	(204,000)
Total income tax expense	46,947,000	45,739,000	39,186,000
Business Acquisition [Line Items]
Liability for Uncertain Tax Positions, Current	0	$ 0	$ 0
ExpensAble [Member]
Business Acquisition [Line Items]
Operating Loss Carryforwards	$ 2,800,000
Minimum [Member] | ExpensAble [Member]
Business Acquisition [Line Items]
Net operating loss carryforwards, expiration date	Jan. 01, 2023
Maximum [Member] | ExpensAble [Member]
Business Acquisition [Line Items]
Net operating loss carryforwards, expiration date	Jan. 01, 2030