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Income Taxes (Details) $ / shares in Units, $ in Millions, ₩ in Billions | 3 Months Ended
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Mar. 31, 2018 USD ($) $ / shares | Mar. 31, 2018 KRW (₩) | Mar. 31, 2017 USD ($) $ / shares
Income tax provision | $ 7.3 |  | $ 5.0
Effective income tax rate | 19.00% | 19.00% | 13.90%
Effective income tax rate reconciliation, valuation allowance on U.S. deferred tax assets | $ 4.9 |  |
Income tax expense due to change in estimate related to uncertain tax position and adjustment for ASU 2016-09 |  |  | $ 1.2
Special income tax concession period | 5 years | 5 years |
Decrease in foreign income taxes due to special income tax concession | $ (0.1) |  | $ 0.8
Impact of income tax concession on basic earnings per common share (in dollars per share) | $ / shares | $ 0 |  | $ 0.01
Impact of income tax concession on diluted earnings per common share (in dollars per share) | $ / shares | $ 0 |  | $ 0.01
Tax Authority, South Korea (SRTO) |  |  |
Income tax assessment notice, amount | $ 10.6 | ₩ 11.3 |
Without income tax benefit adjustment and valuation allowance |  |  |
Effective income tax rate | 31.70% | 31.70% | 10.60%

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- Definition Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 + Details
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- Definition The amount of estimated penalties recognized in the period arising from income tax examinations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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