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v2.4.1.9

Operating Leases (Details Textual) (USD $) | 12 Months Ended
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Dec. 31, 2014 sqft Location | Dec. 31, 2015 sqft
Operating Leased Assets [Line Items] |  |
Lessee Leasing Agreements, Operating Leases, Area under Lease | 36,700 dhil_LesseeLeasingAgreementsOperatingLeasesAreaunderLease |
Operating Lease Expense Excluding Rent | $ 300,000 dhil_OperatingLeaseExpenseExcludingRent |
Number of office space locations | 3 us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits |
Operating Leases, Future Minimum Payments Due | 6,282,000 us-gaap_OperatingLeasesFutureMinimumPaymentsDue |
Contractual Reimbursement of Future Minimum Lease Payments Expected Over Life of Operating Lease Agreement | $ 300,000 dhil_ContractualReimbursementofFutureMinimumLeasePaymentsExpectedOverLifeofOperatingLeaseAgreement |
Scenario, Forecast [Member] |  |
Operating Leased Assets [Line Items] |  |
Lessee Leasing Agreements, Operating Leases, Area under Lease |  | 42,400 dhil_LesseeLeasingAgreementsOperatingLeasesAreaunderLease / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember

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- Definition Contractual Reimbursement of Future Minimum Lease Payments Expected Over Life of Operating Lease Agreement + References No definition available. + Details
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Namespace Prefix: | dhil_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Lessee Leasing Agreements, Operating Leases, Area under Lease + References No definition available. + Details
Name: | dhil_LesseeLeasingAgreementsOperatingLeasesAreaunderLease
Namespace Prefix: | dhil_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | duration

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- Definition Operating Lease Expense Excluding Rent + References No definition available. + Details
Name: | dhil_OperatingLeaseExpenseExcludingRent
Namespace Prefix: | dhil_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_OperatingLeasedAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 3) -URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697 + Details
Name: | us-gaap_OperatingLeasesFutureMinimumPaymentsDue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The number of units (items of property) under operating lease arrangements. + References No definition available. + Details
Name: | us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits
Namespace Prefix: | us-gaap_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |