Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 78,521	$ 83,416
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	301	288
Depreciation expense	15,899	15,123
Stock-based compensation expense—restricted stock and stock units	9,857	10,348
Excess tax benefits from stock-based compensation	0	(395)
Deferred income taxes	10,556	(835)
Provision for doubtful accounts	1,697	1,226
Changes in assets and liabilities:
Decrease (increase) in accounts receivable	4,296	(25,379)
Decrease in accounts payable, accrued expenses, accrued payroll and benefit costs	(7,498)	(35,101)
Increase in income taxes payable	27,860	42,278
Change in other assets, net of change in other liabilities	(17,989)	(12,483)
Net cash flows provided by operating activities	123,500	78,486
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(10,335)	(18,810)
Payments to trusts for employee deferred compensation plans	(4,939)	(5,357)
Net cash flows used in investing activities	(15,274)	(24,167)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchases of common stock	(80,687)	(40,182)
Cash dividends paid	(30,597)	(28,748)
Payments for notes payable and other indebtedness	(41)	(38)
Excess tax benefits from stock-based compensation	0	395
Proceeds from exercises of stock options	0	60
Net cash flows used in financing activities	(111,325)	(68,513)
Effect of exchange rate changes on cash and cash equivalents	3,041	3,736
Net decrease in cash and cash equivalents	(58)	(10,458)
Cash and cash equivalents at beginning of period	260,201	224,577
Cash and cash equivalents at end of period	260,143	214,119
Non-cash items:
Stock repurchases awaiting settlement	$ 2,298	$ 3,120