Foreign Currency Gain, (Loss), Net - Additional Information (Detail) $ in Thousands	Jun. 30, 2018 USD ($) ₩ / $	Dec. 31, 2017 USD ($) ₩ / $
Foreign Currency Transaction [Abstract]
Exchange rates using first base rate \| ₩ / $	1,121.7	1,071.4
Intercompany loan balances \| $	$ 685,098	$ 677,267

Foreign exchange rate used to translate amounts denominated in functional currency to reporting currency.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6897108&loc=SL6897125-166521

Name:	us-gaap_ForeignCurrencyExchangeRateTranslation1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant