Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 243,537	$ 265,601
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	1,147	928
Depreciation expense	47,916	46,771
Stock-based compensation expense—restricted stock and stock units	31,163	32,803
Excess tax benefits from stock-based compensation	0	(812)
Deferred income taxes	(13,309)	(8,537)
Provision for doubtful accounts	5,327	3,323
Changes in assets and liabilities:
Increase in accounts receivable	(21,810)	(39,723)
Increase in accounts payable, accrued expenses, accrued payroll and benefit costs	65,745	58,801
Increase in income taxes payable	32,320	12,498
Change in other assets, net of change in other liabilities	(3,573)	(11,233)
Net cash flows provided by operating activities	388,463	360,420
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments for acquisitions, net of cash acquired	(1,699)	(1,900)
Capital expenditures	(28,540)	(63,280)
Payments to trusts for employee deferred compensation plans	(23,837)	(17,835)
Net cash flows used in investing activities	(54,076)	(83,015)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchases of common stock	(167,342)	(126,326)
Cash dividends paid	(91,078)	(85,962)
Payments for notes payable and other indebtedness	(124)	(114)
Excess tax benefits from stock-based compensation	0	812
Proceeds from exercises of stock options	0	223
Net cash flows used in financing activities	(258,544)	(211,367)
Effect of exchange rate changes on cash and cash equivalents	12,292	1,836
Net increase in cash and cash equivalents	88,135	67,874
Cash and cash equivalents at beginning of period	260,201	224,577
Cash and cash equivalents at end of period	348,336	292,451
Non-cash items:
Stock repurchases awaiting settlement	$ 0	$ 9,219