Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 343,389	$ 357,796	$ 305,928
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	1,237	192	557
Depreciation expense	63,078	53,273	49,124
Stock-based compensation expense—restricted stock and stock units	42,699	41,292	40,821
Excess tax benefits from stock-based compensation	(1,822)	(8,762)	(7,174)
Deferred income taxes	(1,868)	(8,579)	(3,643)
Provision for doubtful accounts	9,192	12,005	9,825
Changes in assets and liabilities, net of effects of acquisitions:
Increase in accounts receivable	(15,888)	(75,745)	(134,917)
Increase in accounts payable, accrued expenses, accrued payroll and benefit costs	19,726	60,232	71,740
(Decrease) increase in income taxes payable	(8,246)	19,948	16,359
Change in other assets, net of change in other liabilities	(9,416)	(13,416)	(7,922)
Net cash flows provided by operating activities	442,081	438,236	340,698
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments for acquisitions, net of cash acquired	(2,200)	(14,668)	0
Capital expenditures	(82,956)	(75,057)	(62,830)
Payments to trusts for employee deferred compensation plans	(27,079)	(28,225)	(25,811)
Net cash flows used in investing activities	(112,235)	(117,950)	(88,641)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchases of common stock	(176,031)	(271,138)	(153,821)
Cash dividends paid	(114,164)	(107,561)	(97,604)
Decrease in notes payable and other indebtedness	(154)	(140)	(128)
Excess tax benefits from stock-based compensation	1,822	8,762	7,174
Proceeds from exercises of stock options	223	1,529	14,324
Net cash flows used in financing activities	(288,304)	(368,548)	(230,055)
Effect of exchange rate changes on cash and cash equivalents	(5,918)	(14,280)	(10,647)
Net increase (decrease) in cash and cash equivalents	35,624	(62,542)	11,355
Cash and cash equivalents at beginning of period	224,577	287,119	275,764
Cash and cash equivalents at end of period	260,201	224,577	287,119
Cash paid during the year for:
Interest	266	285	330
Income taxes, net of refunds	219,415	212,668	178,375
Non-cash items:
Stock repurchases awaiting settlement	$ 14,688	$ 11,935	$ 30,152