Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 45,863	$ 98,682	$ 64,581
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,667	14,268	13,940
Bad debt provision	10,483	9,636	25,480
Deferred income tax benefit (expense)	3,074	(5,893)	(684)
Share-based compensation expense	8,827	7,872	6,865
Amortization of premium on marketable securities	2,275	1,822	1,434
Unrealized gain on deferred compensation fund investments	(6,397)	(9,390)	(7,257)
Loss on sale of assets	1,469	1,335	0
Changes in operating assets and liabilities:
Accounts and notes receivable	(37,185)	46,158	(29,532)
Inventories and supplies	5,599	4,931	4,765
Prepaid expenses and other assets	(12,250)	(756)	3,480
Deferred compensation funding	6,661	(52)	(738)
Accounts payable and other accrued expenses	10,244	(7,250)	(9,532)
Accrued payroll, accrued and withheld payroll taxes	(22,189)	59,527	3,517
Income taxes receivable	(8,420)	(8,075)	7,845
Accrued insurance claims	6,966	(5,194)	8,482
Deferred compensation liability	7,421	9,592	935
Net cash provided by operating activities	37,108	217,213	93,581
Cash flows from investing activities:
Disposals of fixed assets	211	274	199
Additions to property and equipment	(5,687)	(4,341)	(4,368)
Purchases of marketable securities	(20,335)	(39,047)	(33,544)
Sales of marketable securities	26,697	6,269	21,256
Cash paid for acquisitions	(23,876)	0	0
Net cash used in investing activities	(22,990)	(36,845)	(16,457)
Cash flows from financing activities:
Dividends paid	(62,226)	(60,705)	(58,951)
Reissuance of treasury stock pursuant to Dividend Reinvestment Plan	92	93	90
Proceeds from the exercise of stock options	2,425	2,920	3,628
Purchases of treasury stock	(21,535)	0	0
Repayments of short-term borrowings, net	0	(10,000)	(20,000)
Payments of statutory withholding on net issuance of restricted stock units	(1,410)	(675)	(587)
Net cash used in financing activities	(82,654)	(68,367)	(75,820)
Net change in cash and cash equivalents	(68,536)	112,001	1,304
Cash and cash equivalents at beginning of the period	139,330	27,329	26,025
Cash and cash equivalents at end of the period	70,794	139,330	27,329
Supplementary cash flow information:
Cash paid for interest	1,385	1,374	3,459
Cash paid for income taxes, net of refunds	21,233	44,865	20,026
Contingent shares settled pursuant to acquisition	0	0	1,012
Accrued variable consideration for acquisition of businesses	$ 10,456	$ 0	$ 0