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Significant Accounting Policies - Narrative (Detail) (USD $) | 3 Months Ended |
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Mar. 31, 2015 Segment | Mar. 31, 2014 | Dec. 31, 2014
Business Organization And Significant Accounting Policies [Line Items] |  |  |
Number of business segment | 1 us-gaap_NumberOfOperatingSegments |  |
Allowance for doubtful accounts | $ 0 us-gaap_AllowanceForDoubtfulAccountsReceivable |  | $ 0 us-gaap_AllowanceForDoubtfulAccountsReceivable
Transfers between fair value levels | 0 dhil_FairValueTransfersBetweenLevel1Level2orLevel3Amount |  | 0 dhil_FairValueTransfersBetweenLevel1Level2orLevel3Amount
Client Performance Period | 5 years |  |
Advance commissions amortization period | 12 months |  |
Contractual Expense Reimburse, Net | 547,755 dhil_ContractualExpenseReimburseNet | 398,248 dhil_ContractualExpenseReimburseNet |
Liability for Uncertain Tax Positions, Current | 0 us-gaap_LiabilityForUncertainTaxPositionsCurrent |  | 0 us-gaap_LiabilityForUncertainTaxPositionsCurrent
Class A, C, and I Shares |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |
Rate of Administrative Service Fees | 0.24%dhil_RateOfAdministrativeServiceFees / us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis = dhil_ClassACandISharesMember |  | 0.25%dhil_RateOfAdministrativeServiceFees / us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis = dhil_ClassACandISharesMember
Class Y |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |
Rate of Administrative Service Fees | 0.10%dhil_RateOfAdministrativeServiceFees / us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis = dhil_ClassYMember |  | 0.10%dhil_RateOfAdministrativeServiceFees / us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis = dhil_ClassYMember
Mutual Funds | Money Market Funds | Level 1 Inputs |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |
Cash Equivalent Fair Value | 26,600,000 dhil_CashEquivalentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentIssuerAxis = dhil_MutualFundsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MoneyMarketFundsMember |  | 31,800,000 dhil_CashEquivalentFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / invest_InvestmentIssuerAxis = dhil_MutualFundsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MoneyMarketFundsMember
Incentive Fees Method One [Member] |  |  |
Business Organization And Significant Accounting Policies [Line Items] |  |  |
Performance Incentive Fees | $ 0 us-gaap_PerformanceFees / us-gaap_IncomeStatementLocationAxis = dhil_IncentiveFeesMethodOneMember | $ 0 us-gaap_PerformanceFees / us-gaap_IncomeStatementLocationAxis = dhil_IncentiveFeesMethodOneMember |

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- Definition For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 4 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.4) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. + References No definition available. + Details
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