Gross Amounts Associated With Derivative Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Interest Rate Swap
Derivative [Line Items]
Liabilities	$ 220,040	$ 243,945
Liabilities, Cash Collateral Posted	238,180	281,021
Liabilities, Net Amount	(18,140)	(37,076)
Forward Purchase Commitments
Derivative [Line Items]
Assets	6,476	5,452
Assets, Net Amount	6,476	5,452
Futures Contracts
Derivative [Line Items]
Assets	51
Assets, Cash Collateral Posted	1,237
Assets, Net Amount	$ (1,186)

Fair value of liability associated with derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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- Definition

Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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- Definition

Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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