Financial Instruments with Off-Balance Sheet Risk and Derivatives (Company's Interest Rate Swaps) (Detail) - Swap - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Notional Amount	$ 20,400,000	$ 20,900,000
Estimated Fair Value	$ 1,400,000	$ 1,500,000

Fair value of the assets less the liabilities of a derivative or group of derivatives.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Name Accounting Standards Codification

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant