Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 341,591	$ 320,724
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	1,022	1,334
Depreciation expense	48,485	48,344
Stock-based compensation expense—restricted stock and stock units	34,803	33,000
Deferred income taxes	(9,685)	(8,427)
Provision for doubtful accounts	6,501	8,210
Changes in assets and liabilities:
Increase in accounts receivable	(72,288)	(119,096)
Increase in accounts payable, accrued expenses, accrued payroll and benefit costs	99,629	131,874
(Decrease) increase in income taxes payable	(6,734)	18,339
Change in other assets, net of change in other liabilities	(4,318)	14,975
Net cash flows provided by operating activities	439,006	449,277
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(45,138)	(27,186)
Payments to trusts for employee deferred compensation plans	(28,391)	(27,984)
Net cash flows used in investing activities	(73,529)	(55,170)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchases of common stock	(214,047)	(216,401)
Cash dividends paid	(109,702)	(102,696)
Payments for notes payable and other indebtedness	(148)	(136)
Net cash flows used in financing activities	(323,897)	(319,233)
Effect of exchange rate changes on cash and cash equivalents	(5,418)	(7,887)
Net increase in cash and cash equivalents	36,162	66,987
Cash and cash equivalents at beginning of period	276,579	294,753
Cash and cash equivalents at end of period	312,741	361,740
Non-cash items:
Stock repurchases awaiting settlement	$ 5,482	$ 7,043