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Stockholders' equity - Additional Information (Detail) (USD $) | 12 Months Ended | 1 Months Ended
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Jun. 11, 2014 | Jun. 06, 2014 | Mar. 07, 2011 | Mar. 04, 2011 | Jul. 07, 2010
Stockholders Equity [Line Items] |  |  |  |  |  |  |
Common Stock, Shares, Issued | 32,312,276 us-gaap_CommonStockSharesIssued | 25,070,386 us-gaap_CommonStockSharesIssued |  |  |  |  |
Common Stock, Par Or Stated Value Per Share | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare |  |  |  |  |
Investment Warrants Expiration Date | Jul. 07, 2016 |  |  |  |  |  |
Proceeds From Issuance Of Common Stock | $ 15,925,000 us-gaap_ProceedsFromIssuanceOfCommonStock | $ 1,110,000 us-gaap_ProceedsFromIssuanceOfCommonStock |  |  |  |  |
Underwritten Offering [Member] |  |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |  |
Common Stock, Shares, Issued |  |  |  | 6,000,000 us-gaap_CommonStockSharesIssued / us-gaap_StatementClassOfStockAxis = hdsn_UnderwrittenOfferingMember |  |  |
Common Stock, Par Or Stated Value Per Share |  |  |  | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare / us-gaap_StatementClassOfStockAxis = hdsn_UnderwrittenOfferingMember |  |  |
Additional Offering Expenses |  |  | 400,000 hdsn_AdditionalOfferingExpenses / us-gaap_StatementClassOfStockAxis = hdsn_UnderwrittenOfferingMember |  |  |  |
Underwriters [Member] |  |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  | 6,900,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementClassOfStockAxis = hdsn_UnderwritersMember | 6,000,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementClassOfStockAxis = hdsn_UnderwritersMember |  |  |
Share Price |  |  | $ 2.3375 us-gaap_SharePrice / us-gaap_StatementClassOfStockAxis = hdsn_UnderwritersMember | $ 2.3375 us-gaap_SharePrice / us-gaap_StatementClassOfStockAxis = hdsn_UnderwritersMember |  |  |
Purchase Of Additional Common Stock |  |  | 900,000 hdsn_PurchaseOfAdditionalCommonStock / us-gaap_StatementClassOfStockAxis = hdsn_UnderwritersMember | 900,000 hdsn_PurchaseOfAdditionalCommonStock / us-gaap_StatementClassOfStockAxis = hdsn_UnderwritersMember |  |  |
Proceeds From Issuance Of Common Stock |  |  | 16,128,750 us-gaap_ProceedsFromIssuanceOfCommonStock / us-gaap_StatementClassOfStockAxis = hdsn_UnderwritersMember |  |  |  |
Reimbursement Expense |  |  | 150,000 hdsn_ReimbursementExpense / us-gaap_StatementClassOfStockAxis = hdsn_UnderwritersMember |  |  |  |
Public [Member] |  |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |  |
Share Price |  |  |  | $ 2.50 us-gaap_SharePrice / us-gaap_StatementClassOfStockAxis = hdsn_PublicMember |  |  |
Stock Unit |  |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |  |
Common Stock, Shares, Issued |  |  |  |  |  |  | 2,737,500 us-gaap_CommonStockSharesIssued / us-gaap_PlanNameAxis = hdsn_StockUnitMember
2010 Offering |  |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |  |
Common Stock, Shares, Issued |  |  |  |  |  |  | 1,368,750 us-gaap_CommonStockSharesIssued / us-gaap_PlanNameAxis = hdsn_TwoZeroOneZeroOfferingMember
Common Stock, Par Or Stated Value Per Share |  |  |  |  |  |  | $ 2.00 us-gaap_CommonStockParOrStatedValuePerShare / us-gaap_PlanNameAxis = hdsn_TwoZeroOneZeroOfferingMember
Proceeds from Issuance or Sale of Equity |  |  |  |  |  |  | 4,900,000 us-gaap_ProceedsFromIssuanceOrSaleOfEquity / us-gaap_PlanNameAxis = hdsn_TwoZeroOneZeroOfferingMember
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  |  |  | $ 0.60 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 / us-gaap_PlanNameAxis = hdsn_TwoZeroOneZeroOfferingMember | $ 2.60 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 / us-gaap_PlanNameAxis = hdsn_TwoZeroOneZeroOfferingMember
Adjustment of Warrants Granted for Services |  |  |  |  |  |  | $ 1,300,000 us-gaap_AdjustmentOfWarrantsGrantedForServices / us-gaap_PlanNameAxis = hdsn_TwoZeroOneZeroOfferingMember
Class Of Warrant Or Right Repurchase During Period |  |  |  |  |  | 150,000 hdsn_ClassOfWarrantOrRightRepurchaseDuringPeriod / us-gaap_PlanNameAxis = hdsn_TwoZeroOneZeroOfferingMember |
Class Of Warrant Or Right Issued Unit During Period |  |  |  |  | 1,218,750 hdsn_ClassOfWarrantOrRightIssuedUnitDuringPeriod / us-gaap_PlanNameAxis = hdsn_TwoZeroOneZeroOfferingMember |  |
Common Stock |  |  |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |  |  |
Common Stock, Shares, Issued |  |  |  |  |  |  | 2,737,500 us-gaap_CommonStockSharesIssued / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember
Stock Issued During Period, Shares, New Issues | 6,900,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |  |  |

X
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