Goodwill (Key Ratios to Measure Goodwill of Bank Reporting Unit for Impairment) (Detail) (Bank Reporting Unit [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2013 Ratios		May 31, 2012
Goodwill [Line Items]
Key ratios considered in measuring the fair value of the bank reporting unit	3
Goodwill	$ 1,165,200		$ 1,158,248
Fair value of the bank reporting unit exceeded carrying value	44.60%		5.90%
Previous Annual Time Period	12 months
Annual [Member]
Goodwill [Line Items]
Price to book	1.57		1.29
Price to tangible book	1.80		1.47
Price to earnings	22.1	[1]

[1] Last twelve months earnings.