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v3.20.2

Debt - Convertible Notes Narrative (Details) | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | ---
Jun. 30, 2020 USD ($) tradingDays | Sep. 30, 2020 USD ($) $ / shares | Sep. 30, 2019 USD ($) | Sep. 30, 2020 USD ($) $ / shares | Sep. 30, 2019 USD ($) | Jul. 02, 2020 USD ($) | Dec. 31, 2019 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt extinguishment charge |  | $ 0 | $ 0 | $ 21,500,000 | $ 0 |  |
Payment for Debt Extinguishment or Debt Prepayment Cost |  |  |  | 19,100,000 | 0 |  |
Debt issuance costs |  |  |  | 9,100,000 | 0 |  |
Purchase of convertible note capped call |  |  |  | (19,400,000) | $ 0 |  |
Debt instrument, convertible, redemption price as a percent of principal amount | 100.00% |  |  |  |  |  |
Debt instrument, convertible, threshold percentage of stock price trigger | 130.00% |  |  |  |  |  |
Debt instrument, convertible, threshold trading days | tradingDays | 20 |  |  |  |  |  |
Debt instrument, convertible, threshold consecutive trading days | tradingDays | 30 |  |  |  |  |  |
Debt issuance costs |  | 15,200,000 |  | 15,200,000 |  |  | $ 12,300,000
Equity component of convertible note |  | $ 1,100,000 |  | $ 49,800,000 |  |  |
Cap price (in dollars per share) | $ / shares |  | $ 19.76 |  | $ 19.76 |  |  |
[AdditionalPaidInCapitalMember] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Equity component of convertible note |  | $ 1,100,000 |  | $ 49,800,000 |  |  |
Allegheny Technologies 3.5% Convertible Senior Notes due 2025 | Convertible Debt |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate |  | 3.50% |  | 3.50% |  |  |
Debt instrument, face amount, additional amount offered to underwriters | $ 40,000,000.0 |  |  |  |  |  |
Debt instrument, convertible, conversion ratio |  | 0.0645745 |  |  |  |  |
Debt instrument, convertible, conversion price (in dollars per share) | $ / shares |  | $ 15.49 |  | $ 15.49 |  |  |
Debt instrument, interest rate, effective percentage |  | 8.40% |  | 8.40% |  |  |
Debt, Gross | $ 285,000,000.0 | $ 291,400,000 |  | $ 291,400,000 |  | $ 6,400,000 | 0
Equity component of convertible debt |  | 49,000,000.0 |  | 49,000,000.0 |  | $ 51,400,000 | 0
Allegheny Technologies 3.5% Convertible Senior Notes due 2025 | Convertible Debt | Long-term Debt [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt issuance costs |  | 7,500,000 |  | 7,500,000 |  |  |
Allegheny Technologies 3.5% Convertible Senior Notes due 2025 | Convertible Debt | Additional Paid in Capital |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt issuance costs |  | $ 1,600,000 |  | $ 1,600,000 |  |  |
Allegheny Technologies 4.75% Convertible Senior Notes due 2022 |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Interest rate |  | 4.75% |  | 4.75% |  |  |
Debt, Gross |  | $ 84,200,000 |  | $ 84,200,000 |  |  | $ 287,500,000
Allegheny Technologies 4.75% Convertible Senior Notes due 2022 | Convertible Debt |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt instrument, repurchased face amount |  | $ 203,200,000 |  | 203,200,000 |  |  |
Write off of Deferred Debt Issuance Cost |  |  |  | $ 2,400,000 |  |  |

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- Definition Adjustment to additional paid in capital resulting from the recognition of convertible debt instruments as two separate components - a debt component and an equity component. This bifurcation may result in a basis difference associated with the liability component that represents a temporary difference for purposes of applying accounting for income taxes. The initial recognition of deferred taxes for the tax effect of that temporary difference is as an adjustment to additional paid in capital. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 25 -Paragraph 22 -URI http://asc.fasb.org/extlink&oid=51819886&loc=SL6014347-161799 + Details
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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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