Acquisition of Txcell S.A. - Summary of Non-controlling Interest (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Noncontrolling Interest [Abstract]
Non-controlling interest at January 1, 2018	$ 739
Non-controlling interest at Acquisition Date		$ 35,829
Shares acquired post acquisition		(34,516)
Non-controlling interest of acquired entity		1,313
Foreign currency effect		(19)
Loss attributable to non-controlling interest	(53)	(555)
Non-controlling interest at December 31, 2018	$ 686	$ 739