Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 224,410	$ 205,482
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	683	905
Depreciation expense	31,740	32,403
Stock-based compensation expense—restricted stock and stock units	22,914	21,945
Deferred income taxes	(2,015)	(10,188)
Provision for doubtful accounts	3,535	3,950
Changes in assets and liabilities:
Increase in accounts receivable	(50,943)	(80,580)
Increase in accounts payable, accrued expenses, accrued payroll and benefit costs	17,097	45,959
Increase in income taxes payable	4,702	36,215
Change in other assets, net of change in other liabilities	(4,296)	7,873
Net cash flows provided by operating activities	247,827	263,964
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(28,625)	(17,261)
Payments to trusts for employee deferred compensation plans	(19,104)	(19,827)
Net cash flows used in investing activities	(47,729)	(37,088)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchases of common stock	(133,617)	(138,002)
Cash dividends paid	(73,960)	(68,985)
Payments for notes payable and other indebtedness	(98)	(90)
Net cash flows used in financing activities	(207,675)	(207,077)
Effect of exchange rate changes on cash and cash equivalents	438	(5,896)
Net (decrease) increase in cash and cash equivalents	(7,139)	13,903
Cash and cash equivalents at beginning of period	276,579	294,753
Cash and cash equivalents at end of period	269,440	308,656
Non-cash items:
Stock repurchases awaiting settlement	$ 5,691	$ 6,483