This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
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The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 11
-Subparagraph (a)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale 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.

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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.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Summary of Significant Accounting Policies - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2017 USD ($) Segment	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Realized gains and losses on investments	$ 0	$ 0
Other-than-temporary declines in value of marketable securities	0
Impairment losses not recognized	$ 0
Unrecognized tax benefits that would, if recognized, affect the Company’s effective tax rate			$ 0
Number of operating segment \| Segment	1
Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of the assets	3 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of the assets	5 years