CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
OPERATING ACTIVITIES
Net income	$ 122,080	$ 118,963
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	22,431	16,875
Provision for doubtful accounts	3,618	85
Stock-based compensation	12,318	15,179
Deferred income taxes	(2,048)	15,350
Excess tax benefit on stock-based compensation	(9,344)	(13,827)
Loss on sale/disposal of assets	485	180
Changes in operating elements (net of acquisitions):
Receivables	(95,204)	42,295
Prepaid expenses and other	(6,049)	(7,378)
Other non-current assets	(1,016)	0
Accounts payable and outstanding checks	47,201	(22,783)
Accrued compensation	(37,864)	(84,431)
Accrued income taxes	51,949	32,732
Other accrued liabilities	(15,861)	(9,090)
Net cash provided by operating activities	92,696	104,150
INVESTING ACTIVITIES
Purchases of property and equipment	(13,537)	(13,121)
Purchases and development of software	(3,183)	(4,704)
Acquisitions, net of cash acquired	1,780	0
Other	56	(770)
Net cash used for investing activities	(18,444)	(18,595)
FINANCING ACTIVITIES
Proceeds from stock issued for employee benefit plans	15,823	6,990
Stock tendered for payment of withholding taxes	(18,955)	(32,270)
Repurchase of common stock	(28,999)	(21,249)
Cash dividends	(64,597)	(63,888)
Excess tax benefit on stock-based compensation	0	13,827
Proceeds from short-term borrowings	2,450,000	1,480,000
Payments on short-term borrowings	(2,450,000)	(1,460,000)
Net cash used for financing activities	(96,728)	(76,590)
Effect of exchange rates on cash	4,604	2,212
Net (decrease)/increase in cash and cash equivalents	(17,872)	11,177
Cash and cash equivalents, beginning of period	247,666	168,229
Cash and cash equivalents, end of period	229,794	179,406
Noncash transactions from investing and financing activities:
Accrued share repurchases held in other accrued liabilities	3,000	3,000
Accrued purchases of property and equipment	$ 1,404	$ 0