Geographic and Segment Information - Net Sales by Region, Based on Location of Products are Billed (Detail) - USD ($)
$ in Thousands |
3 Months Ended |
6 Months Ended |
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
|
| Total net sales |
$ 199,685
|
$ 166,685
|
$ 365,504
|
$ 328,395
|
| Korea [Member] |
|
|
|
|
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
|
| Total net sales |
58,060
|
67,979
|
112,750
|
133,062
|
| Asia Pacific (Other Than Korea) [Member] |
|
|
|
|
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
|
| Total net sales |
119,725
|
76,524
|
209,430
|
155,988
|
| U.S.A. [Member] |
|
|
|
|
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
|
| Total net sales |
13,593
|
11,155
|
23,411
|
20,322
|
| Europe [Member] |
|
|
|
|
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
|
| Total net sales |
7,619
|
10,725
|
18,597
|
18,578
|
| Others [Member] |
|
|
|
|
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
|
| Total net sales |
$ 688
|
$ 302
|
$ 1,316
|
$ 445
|