Stockholders' Equity - Common Stock Shares Reserved (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Stockholders' Equity
Total (in shares)	46,270,890	39,692,245
2016 Stock Option and Incentive Plan
Stockholders' Equity
Stock-based awards available for grant under 2016 Plan (in shares)	14,957,734	9,313,354
Common Class A
Stockholders' Equity
Class A common stock reserved for Twilio.org (in shares)	795,673	572,676
Class A common stock reserved for the convertible senior notes (in shares)	10,472,165	10,472,165
Stock options issued and outstanding
Stockholders' Equity
Stock options issued and outstanding (in shares)	7,705,848	7,978,369
Nonvested restricted stock units issued and outstanding
Stockholders' Equity
Nonvested restricted stock units issued and outstanding (in shares)	8,490,517	8,262,902
Class A common stock committed under 2016 ESPP
Stockholders' Equity
Stock-based awards available for grant under 2016 Plan (in shares)	3,848,953	3,092,779