Income Taxes - Reconciliation of Provision for Income Taxes at Statutory Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax benefit at federal statutory tax rate	$ 7,929	$ (23,496)	$ (16,388)
Tax benefit at state statutory tax rate	67	(1,008)	(499)
Foreign tax rate differential	(123)	57	(826)
Change in federal statutory tax rate and valuation allowance under U.S. Tax Reform	(185)	0	0
Losses not benefitted/(benefitted)	(15,440)	17,701	9,738
Subsidiary earnings taxed in the US	717	0	0
Meals and entertainment	309	222	44
Stock compensation	6,006	7,857	8,492
Foreign exchange (gains) and losses, net	(776)	0	0
Reserve for tax exposure	1,893	0	0
Nondeductible expenses and other	64	(161)	121
Provision for income taxes	$ 461	$ 1,172	$ 682