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Shareholders' Equity - At-the-Market Offering Program - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Aug. 23, 2017
Stockholders Equity [Line Items]
Maximum aggregate offering price under sales agreement			$ 250,000,000
Direct stock issuance costs	$ 285,000	$ 285,000
Net proceeds from the sale of Common stock	5,391,000	5,391,000
Available amount in sales agreement	$ 244,560,000	$ 244,560,000
Common Stock
Stockholders Equity [Line Items]
Sale of common stock, shares	35,000	35,000

X

- Definition

The cash outflow for cost incurred directly with the issuance of an equity security.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
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The cash inflow from the issuance of an equity stock that has been previously reacquired by the entity.

+ References

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-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
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Number of treasury shares (units) reissued during the period, excluding reissuance of shares (units) held in treasury used to satisfy equity-based compensation obligations exercised by the holders of such rights. Upon reissuance of shares (units) from treasury, either the common or preferred stock (unit) reissued is outstanding.

+ References

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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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Common stock available for sale value.

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Maximum aggregate offering price under sales agreement

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Stockholders Equity [Line Items]

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