Goodwill (Key Ratios to Measure Goodwill of Bank Reporting Unit for Impairment) (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2012	May 31, 2012	May 31, 2011
Annual [Member]
Goodwill [Line Items]
Price to book		1.29	1.36
Price to tangible book		1.47	1.60
Bank Reporting Unit [Member]
Goodwill [Line Items]
Key ratios considered in measuring the fair value of the bank reporting unit	2
Goodwill		$ 1,158,248	$ 915,421
Fair value of the bank reporting unit exceeded carrying value		5.90%	13.00%

Carrying amount of goodwill allocated to the bank reporting unit.

No definition available.

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Key Ratios Considered In Measuring The Fair Value Of The Bank Reporting Unit

No definition available.

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Market multiple used, in part, to determine the fair value of the bank reporting unit.

No definition available.

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Market multiple used, in part, to determine the fair value of the bank reporting unit.

No definition available.

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Percentage By Which Fair Value Of Bank Reporting Unit Exceeded Its Carrying Value

No definition available.

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