Summary of Significant Accounting Policies (Details) (USD $)	3 Months Ended		6 Months Ended
	Nov. 30, 2011	Nov. 30, 2010	Nov. 30, 2011	Nov. 30, 2010	May 31, 2011	May 31, 2010
Accounting Policies [Line Items]
Equity	$ 1,293,814,000	$ 998,465,000	$ 1,293,814,000	$ 998,465,000	$ 1,337,817,000	$ 871,517,000
Number of merchant services segments	2		2
Cash and cash equivalents	770,860,000	663,660,000	770,860,000	663,660,000	1,354,285,000	769,946,000
Number of primary financial institution sponsors	5		5
Settlement processing assets	206,642,000		206,642,000		280,359,000
Settlement processing obligations	(270,290,000)		(270,290,000)		(838,565,000)
Cost of service	185,931,000	154,205,000	377,467,000	305,246,000
Recoverability of guaranteed checks			have not historically recovered 100% of the guaranteed checks
Claims receivable, allowance for losses	4,169,000		4,169,000		3,870,000
Provision for doubtful accounts			13,061,000	10,146,000
Number of reporting units	6		6
Effective tax rate	27.50%	29.60%	30.20%	30.60%
Financing receivable	16,100,000		16,100,000		18,900,000
Diluted Weighted Average Shares Outstanding Reconciliation [Abstract]
Basic weighted average shares outstanding	78,348,000	79,701,000	79,207,000	79,642,000
Plus: dilutive effect of stock options and other share-based awards	528,000	643,000	624,000	670,000
Diluted weighted average shares outstanding	78,876,000	80,344,000	79,831,000	80,312,000
Interchange reimbursement [Member]
Accounting Policies [Line Items]
Settlement processing obligations	203,495,000		203,495,000		212,069,000
Liability to Members [Member]
Accounting Policies [Line Items]
Settlement processing obligations	11,034,000		11,034,000		(718,650,000)
Liability to merchants [Member]
Accounting Policies [Line Items]
Settlement processing obligations	(133,552,000)		(133,552,000)		(129,806,000)
Exception items [Member]
Accounting Policies [Line Items]
Settlement processing obligations	12,943,000		12,943,000		12,394,000
Merchant Reserves [Member]
Accounting Policies [Line Items]
Settlement processing obligations	(358,857,000)		(358,857,000)		(208,195,000)
Fair value of guarantees of customer chargebacks [Member]
Accounting Policies [Line Items]
Settlement processing obligations	(3,817,000)		(3,817,000)		(3,102,000)
Cost of service	2,900,000	1,200,000	5,300,000	2,100,000
Reserves for sales allowances [Member]
Accounting Policies [Line Items]
Settlement processing obligations	(1,536,000)		(1,536,000)		(3,275,000)
interchange reimbursement [Member]
Accounting Policies [Line Items]
Settlement processing assets	26,899,000		26,899,000		72,022,000
Receivable from Members [Member]
Accounting Policies [Line Items]
Settlement processing assets	62,667,000		62,667,000		142,117,000
Receivable from networks [Member]
Accounting Policies [Line Items]
Settlement processing assets	117,406,000		117,406,000		124,980,000
Exception items [Member]
Accounting Policies [Line Items]
Settlement processing assets	959,000		959,000		4,456,000
Merchant Reserves [Member]
Accounting Policies [Line Items]
Cash and cash equivalents	360,100,000		360,100,000		271,400,000
Settlement processing assets	(1,289,000)		(1,289,000)		(63,216,000)
Check guarantee loss reserve [Member]
Accounting Policies [Line Items]
Claims receivable, allowance for losses	4,200,000		4,200,000		3,900,000
Provision for doubtful accounts	3,400,000	3,700,000	7,800,000	7,900,000
Hardware and Software [Member]
Accounting Policies [Line Items]
Property plant and equipment						54,900,000
Customer-related [Member]
Accounting Policies [Line Items]
Intangible assets, useful life, maximum (in years)			30
Stock Options [Member]
Accounting Policies [Line Items]
Antidilutive securities excluded from computation of diluted share base (in shares)	600,000	1,000,000	400,000	1,000,000
Notes Payable [Member] | UCS [Member]
Accounting Policies [Line Items]
Interest rate, range, minimum			8.00%
Interest rate, range, maximum			10.00%
UNITED KINGDOM
Accounting Policies [Line Items]
Effective income tax rate reconciliation, change in enacted tax rate			2.00%	1.00%
Change In Accounting Principle For The Retirement of Share Repurchases [Member]
Accounting Policies [Line Items]
Retrospective adjustment for the correction of an error and change in accounting method					0
Paid-in Capital [Member]
Accounting Policies [Line Items]
Equity	342,914,000	385,970,000	342,914,000	385,970,000	419,591,000	390,325,000
Paid-in Capital [Member] | Change In Accounting Principle For The Retirement of Share Repurchases [Member]
Accounting Policies [Line Items]
Retrospective adjustment for the correction of an error and change in accounting method					29,578,000	29,578,000
Paid-in Capital [Member] | Adjustment for correction error [Member]
Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets					112,980,000	100,000,000
Treasury Stock [Member]
Accounting Policies [Line Items]
Equity	0	0	0	0	0	0
Treasury Stock [Member] | Change In Accounting Principle For The Retirement of Share Repurchases [Member]
Accounting Policies [Line Items]
Retrospective adjustment for the correction of an error and change in accounting method					0
Treasury Stock [Member] | Adjustment for correction error [Member]
Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets					(112,980,000)	(100,000,000)
Retained Earnings [Member]
Accounting Policies [Line Items]
Equity	790,532,000	607,016,000	790,532,000	607,016,000	685,624,000	515,194,000
Retained Earnings [Member] | Change In Accounting Principle For The Retirement of Share Repurchases [Member]
Accounting Policies [Line Items]
Retrospective adjustment for the correction of an error and change in accounting method					(29,578,000)	(29,578,000)
Previously Reported [Member]
Accounting Policies [Line Items]
Equity					1,337,817,000	871,517,000
Previously Reported [Member] | Paid-in Capital [Member]
Accounting Policies [Line Items]
Equity					502,993,000	460,747,000
Previously Reported [Member] | Treasury Stock [Member]
Accounting Policies [Line Items]
Equity					(112,980,000)	(100,000,000)
Previously Reported [Member] | Retained Earnings [Member]
Accounting Policies [Line Items]
Equity					$ 715,202,000	$ 544,772,000