Basis of Presentation - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Segment	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Nature Of Operations [Line Items]
Number of operating segments | Segment			2
Net foreign exchange (losses) gains resulting from foreign currency transactions included in other income	$ (45,000)	$ 11,000	$ (98,000)	$ (24,000)
Cumulative-effect adjustment to retained earnings					$ 510,000
Adjustments of deferred tax assets	13,500,000		13,500,000		13,300,000
Adjustments of deferred tax valuation allowance			0	$ 7,600,000	12,600,000
Retained Earnings [Member]
Nature Of Operations [Line Items]
Cumulative-effect adjustment to retained earnings					$ 510,000
ASU No. 2016-09 [Member]
Nature Of Operations [Line Items]
Deferred tax assets	600,000		600,000
Adjustments of deferred tax assets	100,000		100,000
Adjustments of deferred tax valuation allowance			200,000
ASU No. 2016-09 [Member] | Retained Earnings [Member]
Nature Of Operations [Line Items]
Cumulative-effect adjustment to retained earnings	$ 500,000		$ 500,000