Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 265,601	$ 264,353
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	928	0
Depreciation expense	46,771	39,487
Stock-based compensation expense—restricted stock and stock units	32,803	30,540
Excess tax benefits from stock-based compensation	(812)	(4,645)
Deferred income taxes	(8,537)	(6,912)
Provision for doubtful accounts	3,323	7,096
Changes in assets and liabilities:
Increase in accounts receivable	(39,723)	(96,505)
Increase in accounts payable, accrued expenses, accrued payroll and benefit costs	58,801	63,149
Increase in income taxes payable	12,498	34,854
Change in other assets, net of change in other liabilities	(11,233)	(11,176)
Net cash flows provided by operating activities	360,420	320,241
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments for acquisitions, net of cash acquired	(1,900)	0
Capital expenditures	(63,280)	(48,276)
Payments to trusts for employee deferred compensation plans	(17,835)	(19,578)
Net cash flows used in investing activities	(83,015)	(67,854)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchases of common stock	(126,326)	(201,209)
Cash dividends paid	(85,962)	(80,169)
Payments for notes payable and other indebtedness	(114)	(104)
Excess tax benefits from stock-based compensation	812	4,645
Proceeds from exercises of stock options	223	1,511
Net cash flows used in financing activities	(211,367)	(275,326)
Effect of exchange rate changes on cash and cash equivalents	1,836	(12,362)
Net increase (decrease) in cash and cash equivalents	67,874	(35,301)
Cash and cash equivalents at beginning of period	224,577	287,119
Cash and cash equivalents at end of period	292,451	251,818
Non-cash items:
Stock repurchases awaiting settlement	$ 9,219	$ 1,682