Income Taxes - NOLs (Details) $ in Millions	Sep. 30, 2017 USD ($)
Income Tax Disclosure [Abstract]
Maximum net operating losses and credit equivalents available for use in 2017	$ 218.7

Maximum amount of net operating loss carryforwards and credit equivalents available to reduce future taxable income under enacted tax laws in the first year.

No definition available.

Name:	ecyt_MaximumPotentialUseOfNetOperatingLossCarryforwardsAndCreditEquivalentsInYearOne
Namespace Prefix:	ecyt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant