CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING ACTIVITIES
Net income	$ 509,699	$ 449,711	$ 415,904
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	66,409	57,009	56,882
Provision for doubtful accounts	11,538	15,092	15,587
Stock-based compensation	57,661	47,861	9,094
Gain on divestiture	0	(1,848)	0
Deferred income taxes	(17,095)	(3,117)	25,226
Other	7,409	710	314
Other long-term liabilities	0	0	5
Changes in operating elements, net of effects of acquisitions:
Receivables	107,560	(137,102)	(87,316)
Prepaid expenses and other	(228)	6,294	(5,254)
Other non-current assets	741	380	0
Accounts payable and outstanding checks	(53,272)	40,251	47,488
Accrued compensation and profit-sharing contribution	18,580	40,236	(15,097)
Accrued income taxes	5,178	(4,370)	(105,857)
Other accrued liabilities	4,156	2,319	(9,199)
Net cash provided by operating activities	718,336	513,426	347,777
INVESTING ACTIVITIES
Purchases of property and equipment	(28,115)	(22,364)	(40,354)
Purchases and development of software	(16,527)	(7,138)	(7,852)
Acquisitions, net of cash acquired	(369,833)	0	19,126
Restricted cash	359,388	(359,388)	0
Other	641	(6)	221
Net cash used for investing activities	(54,446)	(388,896)	(28,859)
FINANCING ACTIVITIES
Proceeds from stock issued for employee benefit plans	15,557	11,942	15,166
Stock tendered for payment of withholding taxes	(11,368)	(12,604)	(50,144)
Payment of contingent purchase price	0	0	(927)
Repurchase of common stock	(229,863)	(164,041)	(757,305)
Cash dividends	(235,615)	(215,008)	(220,257)
Excess tax benefit on stock-based compensation	8,548	7,558	27,209
Proceeds from short-term borrowings	6,833,000	4,823,000	4,165,023
Payments on short-term borrowings	(6,988,000)	(4,593,000)	(4,043,669)
Debt issuance costs	0	(1,484)	0
Proceeds from long-term borrowings	0	0	500,000
Net cash used for financing activities	(607,741)	(143,637)	(364,904)
Effect of exchange rates on cash	(16,860)	(14,000)	(1,986)
Net change in cash and cash equivalents	39,289	(33,107)	(47,972)
Cash and cash equivalents, beginning of year	128,940	162,047	210,019
Cash and cash equivalents, end of year	168,229	128,940	162,047
Cash paid for income taxes	311,800	271,979	313,799
Cash paid for interest	$ 28,537	$ 27,066	$ 3,875