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Operating Leases - Narrative (Detail) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2015 sqft Location | Dec. 31, 2014 | Dec. 31, 2015
Operating Leased Assets [Line Items] |  |  |
Area of operating lease | 42,400 dhil_LesseeLeasingAgreementsOperatingLeasesAreaunderLease |  |
Operating Lease Expense Excluding Rent |  | $ 300,000 dhil_OperatingLeaseExpenseExcludingRent |
Number of office space locations | 2 us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits |  |
Total future lease payments due | 6,107,000 us-gaap_OperatingLeasesFutureMinimumPaymentsDue |  |
Contractual Reimbursement of Lease Payments Expected Over Life of Lease | 300,000 dhil_ContractualReimbursementofFutureMinimumLeasePaymentsExpectedOverLifeofOperatingLeaseAgreement |  |
Lease Forecast |  |  |
Operating Leased Assets [Line Items] |  |  |
Operating Lease Expense Excluding Rent |  |  | $ 400,000 dhil_OperatingLeaseExpenseExcludingRent / 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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- Definition Lessee Leasing Agreements, Operating Leases, Area under Lease + References No definition available. + Details
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- Definition Operating Lease Expense Excluding Rent + References No definition available. + Details
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- Details
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Balance Type: | na
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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
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- Definition The number of units (items of property) under operating lease arrangements. + References No definition available. + Details
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- Details
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