Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net income	$ 47,268	$ 38,079	$ 33,765
Reconciliations of net income to net cash provided by (used in) operating activities:
Depreciation and amortization	6,228	5,326	4,844
Non-cash operating lease expense	6,955	8,045	7,246
Investment amortization and losses recognized	1,859	1,433	587
Loss recognized on disposal of property and equipment	139	114	574
Deferred income taxes	(2,169)	(347)	5,492
Share-based compensation	7,390	5,366	3,436
Changes in certain operating assets and liabilities:
Trade accounts receivable	(8,131)	(37,201)	45,055
Income taxes	(1,063)	8,158	(5,150)
Prepaid expenses and other	(2,181)	(1,645)	(1,042)
Accounts payable	3,779	(261)	(1,247)
Accrued payroll, payroll taxes and related benefits	24,916	49,739	(22,608)
Other accrued liabilities	15,725	7,753	(1,671)
Workers' compensation claims liabilities	(64,222)	(77,640)	(80,783)
Safety incentives liability	(2,273)	(14,505)	(9,123)
Operating lease liabilities	(6,740)	(7,886)	(7,062)
Other assets and liabilities, net	298	13	(228)
Net cash provided by (used in) operating activities	27,778	(15,459)	(27,915)
Cash flows from investing activities:
Purchase of property, equipment and software	(15,973)	(6,801)	(8,610)
Purchase of investments		(54,835)	(65,738)
Proceeds from sales and maturities of investments	18,732	75,256	47,922
Purchase of restricted investments	(4,345)	(253,781)	(34,968)
Proceeds from sales and maturities of restricted investments	62,740	127,298	65,535
Net cash provided by (used in) investing activities	61,154	(112,863)	4,141
Cash flows from financing activities:
Proceeds from credit-line borrowings		2,718
Payments on credit-line borrowings		(2,718)
Payments on long-term debt	(3,510)	(221)	(220)
Repurchase of common stock	(47,168)	(17,287)	(8,056)
Common stock repurchased on vesting of stock awards	(1,692)	(1,465)	(1,417)
Dividends paid	(8,524)	(9,069)	(9,121)
Proceeds from exercise of stock options	711	1,156	3,084
Net cash used in financing activities	(60,183)	(26,886)	(15,730)
Net increase (decrease) in cash, cash equivalents and restricted cash	28,749	(155,208)	(39,504)
Cash, cash equivalents and restricted cash, beginning of period	78,629	233,837	273,341
Cash, cash equivalents and restricted cash, end of period	$ 107,378	$ 78,629	$ 233,837