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Retirement Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Retirement plan, employees maximum pre-tax contributions percentage	60.00%
Contributions to 401(k) plan	$ 0	$ 0	$ 0

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- References

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- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

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- Definition

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

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