| For the Year Ended December 31 | ||||||||||||||||
| 2015 | 2016 | 2017 | ||||||||||||||
| NT$ | NT$ | NT$ | US$ (Note 4) | |||||||||||||
| Balance at January 1 | $ | 778,866 | $ | 741,089 | $ | 904,790 | $ | 30,526 | ||||||||
| Purchases | 2,010 | 495,928 | 2,649 | 89 | ||||||||||||
| Total gain or loss | ||||||||||||||||
| In profit or loss | (15,891 | ) | (100,734 | ) | 28 | 1 | ||||||||||
| In other comprehensive income | 21,195 | (202,565 | ) | 17,284 | 583 | |||||||||||
| Disposals | (45,091 | ) | (28,928 | ) | (16,202 | ) | (547 | ) | ||||||||
| Balance at December 31 | $ | 741,089 | $ | 904,790 | $ | 908,549 | $ | 30,652 | ||||||||