Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 61,051us-gaap_NetIncomeLoss	$ 51,537us-gaap_NetIncomeLoss	$ 11,030us-gaap_NetIncomeLoss
Non-cash items included in net income:
Deferred income tax expense	12,403
Depreciation and amortization and other	821us-gaap_DepreciationAndAmortization	439us-gaap_DepreciationAndAmortization	307us-gaap_DepreciationAndAmortization
Stock-based compensation	8,137us-gaap_ShareBasedCompensation	6,459us-gaap_ShareBasedCompensation	7,437us-gaap_ShareBasedCompensation
Deferred rent	1,572us-gaap_StraightLineRent	706us-gaap_StraightLineRent	(140)us-gaap_StraightLineRent
Accretion to interest income and other	(72)	116	194
Changes in operating assets and liabilities:
Accounts receivable	(369)	(5,020)	(3,723)
Other assets	99	(579)	337
Fund management and administration payable	(445)	3,470	(3,111)
Compensation and benefits payable	(186)	12,122	(2,012)
Accounts payable and other liabilities	(381)	874	915
Net cash provided by operating activities	82,630	70,124	11,234
Cash flows from investing activities:
Purchase of fixed assets	(4,894)	(6,211)	(190)
Purchase of investments	(3,225)us-gaap_PaymentsToAcquireInvestments	(3,597)us-gaap_PaymentsToAcquireInvestments	(10,004)us-gaap_PaymentsToAcquireInvestments
Cash acquired on acquisition	1,349
Proceeds from the redemption of investments	939	2,781	7,836
Net cash used in investing activities	(5,831)	(7,027)	(2,358)
Cash flows from financing activities:
Net proceeds from sale of common stock			4,329
Dividends paid	(10,785)us-gaap_PaymentsOfDividends
Shares repurchased	(6,531)	(1,613)	(2,261)
Proceeds from exercise of stock options and warrants	1,544	1,586	4,672
Net cash (used in)/provided by financing activities	(15,772)	(27)	6,740
Decrease in cash flow due to changes in foreign exchange rate	(59)
Net increase in cash and cash equivalents	60,968	63,070	15,616
Cash and cash equivalents-beginning of year	104,316	41,246	25,630
Cash and cash equivalents-end of year	165,284	104,316	41,246
Supplemental disclosure of cash flow information:
Cash paid for taxes	66us-gaap_IncomeTaxesPaidNet	38us-gaap_IncomeTaxesPaidNet	33us-gaap_IncomeTaxesPaidNet
Noncash investing and financing activities:
Cashless exercise of stock options and warrants		$ 267wetf_CashlessExerciseOfStockOptions

The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method.

Name:	us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration