Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands			3 Months Ended		12 Months Ended
	Sep. 30, 2017	Dec. 31, 2015	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Statutory income tax rate						35.00%
Partial unpaid interest amount waiver on intercompany loan								$ 174,000
Income tax benefit recognized		$ 17,800
Tax expense due to change in statutory tax rates, TCJA						$ 13,438
Penalty						4,001	$ 689
Change in net operating loss carry-forwards						6,878
Permanent impairment								(62,334)
Net deferred tax assets		171	$ 264			264	183	171
Deferred tax assets, valuation allowance amount		279,867	251,132			251,132	281,473	279,867	$ 194,739
Net operating loss carry-forwards			770,233			770,233
Net operating loss utilized						$ 417	279	121
Net operating loss expiration date						2037
Income tax benefit, minimum tax amounts refundable, TCJA						$ 381
Income tax expenses (benefits)						1,155	3,744	(15,087)
Recognized interest and penalties as income tax expense						(712)
Total interest and penalties accrued		$ 359	8			8	$ 691	$ 359
Income tax penalties	$ 6,030
Accrued tax penalties	3,336
Employee withholding amounts	548
Administrative fine related to tax audit	$ 2,034
Selling, General and Administrative Expenses [Member]
Income Tax Contingency [Line Items]
Income tax penalties			4,179
Other Receivable [Member]
Income Tax Contingency [Line Items]
Employee withholding amounts			548
Securities and Exchange Commission Actions [Member]
Income Tax Contingency [Line Items]
Settlement charge				$ 3,000		3,000
Scenario, Forecast [Member]
Income Tax Contingency [Line Items]
Statutory income tax rate					21.00%
KNTS Audit [Member]
Income Tax Contingency [Line Items]
Income tax expenses (benefits)						676
Luxembourg Subsidiary [Member]
Income Tax Contingency [Line Items]
Net operating loss carry-forwards			310,975			310,975
Korean Statutory Tax Rate [Member]
Income Tax Contingency [Line Items]
Tax credit carry-forwards			5,639			$ 5,639
Net operating loss carry-forwards, expiration period						The Korean tax credits expire at various dates starting from 2018 to 2022
Dutch [Member]
Income Tax Contingency [Line Items]
Tax credit carry-forwards			14,936			$ 14,936
Net operating loss carry-forwards, expiration period						Indefinite period of time
U.S [Member]
Income Tax Contingency [Line Items]
Tax credit carry-forwards			9			$ 9
Korean Subsidiary [Member]
Income Tax Contingency [Line Items]
Statutory income tax rate						24.20%	24.20%	24.20%
Net operating loss carry-forwards			$ 281,383			$ 281,383
Net operating loss expiration date						2026