Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues:
ETF advisory fees	$ 182,816us-gaap_InvestmentAdvisoryFees	$ 148,594us-gaap_InvestmentAdvisoryFees	$ 84,024us-gaap_InvestmentAdvisoryFees
Other income	946us-gaap_OtherIncome	874us-gaap_OtherIncome	774us-gaap_OtherIncome
Total revenues	183,762us-gaap_Revenues	149,468us-gaap_Revenues	84,798us-gaap_Revenues
Expenses:
Compensation and benefits	40,995us-gaap_LaborAndRelatedExpense	36,210us-gaap_LaborAndRelatedExpense	23,233us-gaap_LaborAndRelatedExpense
Fund management and administration	34,383us-gaap_AssetManagementCosts	35,076us-gaap_AssetManagementCosts	23,020us-gaap_AssetManagementCosts
Marketing and advertising	11,514us-gaap_MarketingAndAdvertisingExpense	8,309us-gaap_MarketingAndAdvertisingExpense	5,363us-gaap_MarketingAndAdvertisingExpense
Sales and business development	6,221us-gaap_BusinessDevelopment	6,474us-gaap_BusinessDevelopment	3,586us-gaap_BusinessDevelopment
Professional and consulting fees	7,578us-gaap_ProfessionalFees	2,748us-gaap_ProfessionalFees	4,603us-gaap_ProfessionalFees
Occupancy, communications, and equipment	3,578	2,784	1,419
Depreciation and amortization	821us-gaap_DepreciationAndAmortization	439us-gaap_DepreciationAndAmortization	307us-gaap_DepreciationAndAmortization
Third party sharing arrangements	594wetf_ThirdPartySharingArrangements	1,368wetf_ThirdPartySharingArrangements	5,468wetf_ThirdPartySharingArrangements
Other	4,530us-gaap_OtherExpenses	4,523us-gaap_OtherExpenses	2,976us-gaap_OtherExpenses
ETF shareholders proxy			3,264wetf_EtfShareholderProxy
Litigation, net			176us-gaap_LitigationSettlementAmount
Exchange listing and offering			353wetf_ExchangeListing
Total expenses	110,214us-gaap_OperatingExpenses	97,931us-gaap_OperatingExpenses	73,768us-gaap_OperatingExpenses
Income before taxes	73,548	51,537	11,030
Income tax expense	12,497us-gaap_IncomeTaxExpenseBenefit
Net income	$ 61,051us-gaap_NetIncomeLoss	$ 51,537us-gaap_NetIncomeLoss	$ 11,030us-gaap_NetIncomeLoss
Net income per share-basic	$ 0.46us-gaap_EarningsPerShareBasic	$ 0.41us-gaap_EarningsPerShareBasic	$ 0.09us-gaap_EarningsPerShareBasic
Net income per share-diluted	$ 0.44us-gaap_EarningsPerShareDiluted	$ 0.37us-gaap_EarningsPerShareDiluted	$ 0.08us-gaap_EarningsPerShareDiluted
Weighted-average common shares-basic	131,770	126,651	122,138
Weighted-average common shares-diluted	138,551	139,797	137,968

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