Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 83,416	$ 77,922
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of intangible assets	288	0
Depreciation expense	15,123	13,006
Stock-based compensation expense—restricted stock and stock units	10,348	8,843
Excess tax benefits from stock-based compensation	(395)	(4,256)
Deferred income taxes	(835)	8,039
Provision for doubtful accounts	1,226	2,551
Changes in assets and liabilities:
Increase in accounts receivable	(25,379)	(22,431)
Decrease in accounts payable, accrued expenses, accrued payroll and benefit costs	(35,101)	(23,234)
Increase in income taxes payable	42,278	37,504
Change in other assets, net of change in other liabilities	(12,483)	(13,464)
Net cash flows provided by operating activities	78,486	84,480
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(18,810)	(13,346)
Payments to trusts for employee deferred compensation plans	(5,357)	(7,455)
Net cash flows used in investing activities	(24,167)	(20,801)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchases of common stock	(40,182)	(59,196)
Cash dividends paid	(28,748)	(27,375)
Payments for notes payable and other indebtedness	(38)	(34)
Excess tax benefits from stock-based compensation	395	4,256
Proceeds from exercises of stock options	60	1,113
Net cash flows used in financing activities	(68,513)	(81,236)
Effect of exchange rate changes on cash and cash equivalents	3,736	(8,677)
Net decrease in cash and cash equivalents	(10,458)	(26,234)
Cash and cash equivalents at beginning of period	224,577	287,119
Cash and cash equivalents at end of period	214,119	260,885
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Stock repurchases awaiting settlement	$ 3,120	$ 11,308