Short-Term Borrowings - Additional Information on Short-Term Borrowings (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Disclosure [Abstract]
Outstanding at December 31	$ 845,742us-gaap_ShortTermBorrowings	$ 680,344us-gaap_ShortTermBorrowings	$ 303,045us-gaap_ShortTermBorrowings
Maximum month-end outstanding balance	1,034,741	680,344	640,768
Average daily outstanding balance	$ 782,033	$ 303,352	$ 284,201
Average rate during the year	0.17%	0.16%	0.22%
Average rate at year end	0.18%	0.15%	0.22%

Average interest rate paid on short term debt during the current period.

No definition available.

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- Details

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Subparagraph a

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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-Section S99

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-Subparagraph (SX 210.5-02.19(a))

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-Publisher FASB

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-Topic 942

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-Section S99

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-Publisher SEC

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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+ Details

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- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

+ References

No definition available.

+ Details

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- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, maximum month-end borrowings during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

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-Name Industry Guide

-Number 3

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-Subsection 2

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- Definition

Weighted average interest rate of short-term debt outstanding.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

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-Number 210

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+ Details

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