Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total revenues	$ 942,311	$ 940,698	$ 920,432
Cost of revenues:
Total cost of revenues	734,058	754,025	761,901
Gross margin	208,253	186,673	158,531
Selling, general and administrative expenses	153,879	145,465	123,138
Depreciation and amortization	3,886	4,219	5,452
Income from operations	50,488	36,989	29,941
Other income (expense):
Investment income, net	12,520	9,077	4,668
Interest expense	(1,789)	(1,052)	(313)
Other, net	(81)	(245)	82
Other income, net	10,650	7,780	4,437
Income before income taxes	61,138	44,769	34,378
Provision for income taxes	12,846	6,707	9,208
Net income	$ 48,292	$ 38,062	$ 25,170
Basic income per common share	$ 6.48	$ 5.18	$ 3.46
Weighted average number of basic common shares outstanding	7,451	7,342	7,275
Diluted income per common share	$ 6.27	$ 4.98	$ 3.33
Weighted average number of diluted common shares outstanding	7,699	7,647	7,551
Professional Employer Service Fees [Member]
Revenues:
Total revenues	$ 819,873	$ 793,399	$ 758,046
Staffing Services [Member]
Revenues:
Total revenues	122,438	147,299	162,386
Direct Payroll Costs [Member]
Cost of revenues:
Total cost of revenues	92,455	111,443	122,533
Payroll Taxes and Benefits [Member]
Cost of revenues:
Total cost of revenues	429,713	407,003	404,687
Workers' Compensation [Member]
Cost of revenues:
Total cost of revenues	$ 211,890	$ 235,579	$ 234,681