Stock-Based Compensation - Summary of RSU Activity (Detail)	9 Months Ended
Sep. 30, 2019 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Unvested at December 31, 2018, Number of Shares	1,736,234
RSUs granted, Number of Shares	708,144
RSUs vested, Number of Shares	(631,252)
Unvested at September 30, 2019, Number of Shares	1,813,126
Vested and unreleased, Number of Shares	104,173
Outstanding at September 30, 2019, Number of Shares	1,917,299
Unvested at December 31, 2018, Weighted Average Grant Date Fair Value \| $ / shares	$ 9.65
RSUs granted, Weighted Average Grant Date Fair Value \| $ / shares	7.79
RSUs vested, Weighted Average Grant Date Fair Value \| $ / shares	9.40
Unvested at September 30, 2019, Weighted Average Grant Date Fair Value \| $ / shares	$ 9.13

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

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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)(1)(ii)
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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Share based compensation arrangement by share based payment award equity instruments other than options vested and unreleased.

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