Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 48,292	$ 38,062	$ 25,170
Reconciliations of net income to net cash provided by operating activities:
Depreciation and amortization	3,886	4,219	5,452
Non-cash operating lease expense	6,991
Investment (accretion) amortization and (gains) losses recognized	1,117	163	(51)
Losses recognized on sale of property		64
Deferred income taxes	2,656	(1,192)	4,039
Share-based compensation	7,173	5,502	4,184
Changes in certain operating assets and liabilities:
Trade accounts receivable	(11,964)	(14,933)	(10,180)
Income taxes	(5,738)	6,089	(4,727)
Prepaid expenses and other	(1,039)	(8,156)	(1,825)
Accounts payable	1,657	(830)	222
Accrued payroll, payroll taxes and related benefits	17,858	(21,863)	28,529
Other accrued liabilities	(11,720)	12,550	1,350
Workers' compensation claims liabilities	25,477	49,632	57,140
Safety incentives liability	(1,260)	678	3,697
Operating lease liabilities	(6,242)
Other assets and liabilities, net	(7)	(201)	(141)
Net cash provided by operating activities	77,137	69,784	112,859
Cash flows from investing activities:
Purchase of property, equipment and software	(10,798)	(5,679)	(3,687)
Proceeds from sale of property		485
Purchase of investments	(54,343)	(1,946)	(6,283)
Proceeds from sales and maturities of investments	88,771	1,885	10,718
Purchase of restricted investments	(9,812)	(108,739)	(381,207)
Proceeds from sales and maturities of restricted investments	52,495	74,650	55,482
Net cash provided by (used in) investing activities	66,313	(39,344)	(324,977)
Cash flows from financing activities:
Proceeds from credit-line borrowings	18,843	8,500	24,899
Payments on credit-line borrowings	(18,843)	(8,500)	(24,899)
Payments on long-term debt	(221)	(220)	(221)
Common stock repurchased on vesting of stock awards	(3,136)	(2,952)	(1,673)
Dividends paid	(8,208)	(7,348)	(7,276)
Proceeds from exercise of stock options	754	577	163
Net cash used in financing activities	(10,811)	(9,943)	(9,007)
Net increase (decrease) in cash, cash equivalents and restricted cash	132,639	20,497	(221,125)
Cash, cash equivalents and restricted cash, beginning of period	140,702	120,205	341,330
Cash, cash equivalents and restricted cash, end of period	$ 273,341	$ 140,702	$ 120,205