Income Taxes - Summary of Components of Income Tax Benefit (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income taxes
Federal									$ 0	$ 0	$ 0
State									0	0	0
Foreign									0	0	0
Deferred income taxes
Federal									0	0	0
State									0	0	0
Foreign									(3,377)	(3,300)	(5,523)
Income tax benefit	$ (823)	$ (781)	$ (883)	$ (890)	$ (963)	$ (738)	$ (741)	$ (858)	$ (3,377)	$ (3,300)	$ (5,523)