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Significant Accounting Policies - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended			9 Months Ended
	Dec. 31, 2014 Segment Financial_Institution	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Related Party Transaction [Line Items]
Cash and cash equivalents maturity period, maximum	90 days
Number of financial institutions	1wetf_NumberOfFinancialInstitutions			1wetf_NumberOfFinancialInstitutions
Accounts receivable related-party	$ 17,288	$ 14,791		$ 17,288
ETF advisory fee revenue	182,816us-gaap_InvestmentAdvisoryFees	148,594us-gaap_InvestmentAdvisoryFees	84,024us-gaap_InvestmentAdvisoryFees
Joint venture agreement date	Jan. 01, 2013
Marketing fees	594us-gaap_MarketingExpense	1,368us-gaap_MarketingExpense	806us-gaap_MarketingExpense
Number of operating segments	1us-gaap_NumberOfOperatingSegments
Boost Issuer PLC [Member]
Related Party Transaction [Line Items]
ETF advisory fee revenue				829
WisdomTree Trust [Member]
Related Party Transaction [Line Items]
ETF advisory fee revenue	$ 181,987	$ 148,594	$ 84,024