Restructuring and Severance - Additional Information (Detail) - USD ($)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2016	Dec. 31, 2017
Restructuring Cost And Reserve [Line Items]
Restructuring and severance	$ 201,000	$ 2,940,000
Scenario, Forecast
Restructuring Cost And Reserve [Line Items]
Restructuring and severance			$ 0
Employee Severance and Facilities
Restructuring Cost And Reserve [Line Items]
Restructuring and severance		$ 2,900,000