Goodwill and Intangible Assets - Changes to Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 2,910	$ 2,910
Foreign currency translation adjustment	(344)	(430)
Accumulated amortization	(1,868)	(1,736)
Balance	698	744
Trademark [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	300	300
Foreign currency translation adjustment	(53)	(53)
Accumulated amortization	(247)	(247)
Developed Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,370	1,370
Foreign currency translation adjustment	(153)	(198)
Accumulated amortization	(907)	(839)
Balance	310	333
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,240	1,240
Foreign currency translation adjustment	(138)	(179)
Accumulated amortization	(714)	(650)
Balance	$ 388	$ 411