Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Equity-based Compensation and Equity Incentive Plans - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Jan. 01, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee unrecognized compensation expense		$ 8,700		$ 8,700
Employee unrecognized compensation cost, period of recognition				2 years 7 months 6 days
Equity-based compensation expense		1,069	$ 1,031	$ 3,094	$ 3,445
Restricted Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee unrecognized compensation expense		1,500		$ 1,500
Employee unrecognized compensation cost, period of recognition				1 year 6 months
Equity-based compensation expense		$ 43	$ 141	$ 95	$ 945
Plan 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in number of shares available for issuance (in shares)	1,270,073
2015 and 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grants		536,808		536,808