Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 158,837	$ 175,032
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	666	602
Depreciation expense	31,845	30,710
Stock-based compensation expense—restricted stock and stock units	20,727	22,093
Excess tax benefits from stock-based compensation	0	(802)
Deferred income taxes	18	(2,070)
Provision for doubtful accounts	3,421	3,213
Changes in assets and liabilities:
Decrease (increase) in accounts receivable	3,376	(29,330)
Increase in accounts payable, accrued expenses, accrued payroll and benefit costs	38	7,215
Increase in income taxes payable	49,229	9,741
Change in other assets, net of change in other liabilities	(10,097)	(9,210)
Net cash flows provided by operating activities	258,060	207,194
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments for acquisitions, net of cash acquired	(1,643)	(1,400)
Capital expenditures	(21,186)	(43,740)
Payments to trusts for employee deferred compensation plans	(15,245)	(11,251)
Net cash flows used in investing activities	(38,074)	(56,391)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchases of common stock	(129,243)	(81,544)
Cash dividends paid	(61,448)	(57,895)
Payments for notes payable and other indebtedness	(82)	(75)
Excess tax benefits from stock-based compensation	0	802
Proceeds from exercises of stock options	0	78
Net cash flows used in financing activities	(190,773)	(138,634)
Effect of exchange rate changes on cash and cash equivalents	8,384	1,968
Net increase in cash and cash equivalents	37,597	14,137
Cash and cash equivalents at beginning of period	260,201	224,577
Cash and cash equivalents at end of period	297,798	238,714
Non-cash items:
Stock repurchases awaiting settlement	$ 1,255	$ 7,392