Employee Benefit Plan - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Defined contribution plan, employer's matching contribution percent	50.00%
Percentage of employer matching contribution to employee contribution	8.00%	6.00%	6.00%
Maximum percentage limit of employee contributions	8.00%	6.00%	6.00%
Defined contribution plan, maximum employer's contribution per employee	$ 4,000	$ 3,000	$ 3,000
Aggregate employers contributions to defined contribution plan	$ 500,000	$ 300,000	$ 300,000

No definition available.

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- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

+ Details

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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

No definition available.

+ Details

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- Definition

Maximum amount the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

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- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

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