Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues	$ 940,698	$ 920,432	$ 840,586
Cost of revenues:
Total cost of revenues	754,025	761,901	695,050
Gross margin	186,673	158,531	145,536
Selling, general and administrative expenses	145,465	123,138	113,342
Depreciation and amortization	4,219	5,452	3,253
Income from operations	36,989	29,941	28,941
Other income (expense):
Investment income, net	9,077	4,668	956
Interest expense	(1,052)	(313)	(807)
Loss on litigation			(3,544)
Other, net	(245)	82	40
Other income (expense), net	7,780	4,437	(3,355)
Income before income taxes	44,769	34,378	25,586
Provision for income taxes	6,707	9,208	6,787
Net income	$ 38,062	$ 25,170	$ 18,799
Basic income per common share	$ 5.18	$ 3.46	$ 2.60
Weighted average number of basic common shares outstanding	7,342	7,275	7,226
Diluted income per common share	$ 4.98	$ 3.33	$ 2.55
Weighted average number of diluted common shares outstanding	7,647	7,551	7,378
Professional Employer Service Fees [Member]
Revenues:
Total revenues	$ 793,399	$ 758,046	$ 673,924
Staffing Services [Member]
Revenues:
Total revenues	147,299	162,386	166,662
Direct Payroll Costs [Member]
Cost of revenues:
Total cost of revenues	111,443	122,533	126,753
Payroll Taxes and Benefits [Member]
Cost of revenues:
Total cost of revenues	407,003	404,687	357,867
Workers' Compensation [Member]
Cost of revenues:
Total cost of revenues	$ 235,579	$ 234,681	$ 210,430