Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Matching contribution by the company to the plan	100.00%
Percentage of employees' eligible compensation	6.00%
Plan name	401(K) plan
General and Administrative [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, compensation expense	$ 0.9	$ 0.7	$ 0.7

Amount of cost for defined contribution plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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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

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

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- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

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- Definition

Name of defined contribution plan designed to provide retirement benefits. Includes, but is not limited to, legal name of plan.

+ References

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