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Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Sep. 30, 2015
Tres Amigas
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment charge on investment	$ 700	$ 746

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References

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



-Publisher FASB



-Name Accounting Standards Codification



-Topic 230



-SubTopic 10



-Section 45



-Paragraph 28



-Subparagraph (b)



-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585



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



-Publisher FASB



-Name Accounting Standards Codification



-Topic 320



-SubTopic 10



-Section 35



-Paragraph 34



-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e25351-111560

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