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Significant Accounting Policies - Summary of Assets Under Management Subject to Fees (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Assets under management (AUM) subject to incentive fees and the incentive fees
Total AUM Subject to Incentive Fees	$ 562,613,027dhil_AssetsUnderManagementIncentiveFees	$ 470,726,000dhil_AssetsUnderManagementIncentiveFees
Incentive Fees Under Method Two
Assets under management (AUM) subject to incentive fees and the incentive fees
Performance Incentive Fees	2,458,080us-gaap_PerformanceFees / us-gaap_IncomeStatementLocationAxis = dhil_IncentiveFeesMethodTwoMember	3,900,649us-gaap_PerformanceFees / us-gaap_IncomeStatementLocationAxis = dhil_IncentiveFeesMethodTwoMember
Incentive Fees Under Method Two | Quarter Ended June 30, 2017
Assets under management (AUM) subject to incentive fees and the incentive fees
Performance Incentive Fees	2,427,031us-gaap_PerformanceFees / us-gaap_IncomeStatementLocationAxis = dhil_IncentiveFeesMethodTwoMember / us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis = dhil_AssetUnderManagementContractualPeriodEndDateMember	3,900,649us-gaap_PerformanceFees / us-gaap_IncomeStatementLocationAxis = dhil_IncentiveFeesMethodTwoMember / us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis = dhil_AssetUnderManagementContractualPeriodEndDateMember
Incentive Fees Under Method Two | Quarter Ended December 31, 2018
Assets under management (AUM) subject to incentive fees and the incentive fees
Performance Incentive Fees	0us-gaap_PerformanceFees / us-gaap_IncomeStatementLocationAxis = dhil_IncentiveFeesMethodTwoMember / us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis = dhil_AssetUnderManagementContractualPeriodEndDate2Member	0us-gaap_PerformanceFees / us-gaap_IncomeStatementLocationAxis = dhil_IncentiveFeesMethodTwoMember / us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis = dhil_AssetUnderManagementContractualPeriodEndDate2Member
Incentive Fees Under Method Two | Quarter Ended September 30, 2019
Assets under management (AUM) subject to incentive fees and the incentive fees
Performance Incentive Fees	$ 31,049us-gaap_PerformanceFees / us-gaap_IncomeStatementLocationAxis = dhil_IncentiveFeesMethodTwoMember / us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis = dhil_AssetUnderManagementContractualPeriodEndDate3Member	$ 0us-gaap_PerformanceFees / us-gaap_IncomeStatementLocationAxis = dhil_IncentiveFeesMethodTwoMember / us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis = dhil_AssetUnderManagementContractualPeriodEndDate3Member

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- Definition

Assets under management (AUM) subject to incentive fees and incentive fees.

+ References

No definition available.

+ Details

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- Details

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- Definition

Amount of revenue earned by the entity based on the investment results achieved. Excludes fees based upon a percentage of the assets under management not performance-related.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.13 (a))

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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