Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 51,972	$ 68,040
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,022	6,342
Bad debt provision	42,387	4,000
Stock-based compensation expense (benefit), net of tax impact from equity compensation plans	3,407	(632)
Amortization of premium on marketable securities	1,007	929
Unrealized gain on deferred compensation fund investments	(3,071)	(3,351)
Changes in operating assets and liabilities:
Accounts and notes receivable	(49,873)	(103,697)
Inventories and supplies	798	(997)
Prepaid expenses and other assets	725	(11,658)
Deferred compensation funding	(1,141)	83
Accounts payable and other accrued expenses	55	(1,102)
Accrued payroll, accrued and withheld payroll taxes	23,202	28,575
Income taxes payable	(14,514)	7,865
Accrued insurance claims	8,249	4,992
Deferred compensation liability	4,284	3,733
Net cash provided by operating activities	74,509	3,122
Cash flows from investing activities:
Disposals of fixed assets	481	264
Additions to property and equipment	(3,739)	(3,962)
Purchases of marketable securities	(13,069)	(22,149)
Sales of marketable securities	8,706	20,354
Cash paid for acquisitions	0	(4,584)
Net cash used in investing activities	(7,621)	(10,077)
Cash flows from financing activities:
Dividends paid	(42,748)	(41,302)
Reissuance of treasury stock pursuant to Dividend Reinvestment Plan	68	71
Proceeds from the exercise of stock options	6,855	10,338
Net (repayments) proceeds from short-term borrowings	(25,423)	25,000
Net cash used in financing activities	(61,248)	(5,893)
Net change in cash and cash equivalents	5,640	(12,848)
Cash and cash equivalents at beginning of the period	9,557	23,853
Cash and cash equivalents at end of the period	$ 15,197	$ 11,005