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Financial Risk Management - Summary of Exposures to Risks, Effects on Profit before Income Tax and Shareholders' Equity (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
10% strengthening in foreign exchange rate [member] |  |  |
Disclosure of detailed information about financial instruments [Line Items] |  |  |
Fluctuation of foreign exchange rate | 10.00% | 10.00% | 10.00%
Income before tax | ₩ (10,132) | ₩ (28,134) | ₩ (52,157)
Shareholders' equity | ₩ (7,273) | ₩ (23,817) | ₩ (45,632)
10% weakening in foreign exchange rate [member] |  |  |
Disclosure of detailed information about financial instruments [Line Items] |  |  |
Fluctuation of foreign exchange rate | (10.00%) | (10.00%) | (10.00%)
Income before tax | ₩ 10,132 | ₩ 28,134 | ₩ 52,157
Shareholders' equity | ₩ 7,273 | ₩ 23,817 | ₩ 45,632
Ten percentage increase in market equity price [Member] |  |  |
Disclosure of detailed information about financial instruments [Line Items] |  |  |
Fluctuation of price | 10.00% | 10.00% | 10.00%
Shareholders' equity | ₩ 686 | ₩ 539 | ₩ 3,469
10% decrease in market equity price [Member] |  |  |
Disclosure of detailed information about financial instruments [Line Items] |  |  |
Fluctuation of price | (10.00%) | (10.00%) | (10.00%)
Shareholders' equity | ₩ (686) | ₩ (539) | ₩ (3,469)
100 basis point increase in market interest rate [Member] |  |  |
Disclosure of detailed information about financial instruments [Line Items] |  |  |
Fluctuation of interest rate | 1.00% | 1.00% | 1.00%
Income before tax | ₩ 1,942 | ₩ (3,456) | ₩ (3,601)
Shareholders' equity | ₩ 4,868 | ₩ (1,673) | ₩ (245)
100 basis point decrease in market interest rate [Member] |  |  |
Disclosure of detailed information about financial instruments [Line Items] |  |  |
Fluctuation of interest rate | 1.00% | 1.00% | 1.00%
Income before tax | ₩ (1,954) | ₩ 3,445 | ₩ 3,615
Shareholders' equity | ₩ (5,198) | ₩ (5,025) | ₩ (5,764)

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