Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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

Share-based Compensation Arrangement by Share-based Payment Award, Options, Canceled, Percentage of Shares Outstanding

+ References

No definition available.

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Percentage of Shares Outstanding

+ References

No definition available.

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- References

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- References

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Stock-Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018	Feb. 28, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 6,981	$ 1,262	$ 11,952	$ 4,066
Performance stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of outstanding options that vested (percent)	90.00%		90.00%
Percentage of outstanding options that were canceled (percent)	10.00%		10.00%
Stock-based compensation expense	$ 3,500
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding RSUs at March 31, 2018 (in shares)	299,000		299,000				259,000
Non-employee Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options granted upon initial election to board (shares)					20,000	30,000
Additional number of options available for grant annually (shares)					15,000	20,000
Employees and Executives \| Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding RSUs at March 31, 2018 (in shares)	159,000		159,000