Net Loss Per Share Attributable to Common Stockholders - Anti-Dilutive Securities (Details) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Anti-dilutive securities
Antidilutive securities (in shares)	19,266,388	22,624,271
Conversion price (in dollars per share)	$ 70.90
Stock options issued and outstanding
Anti-dilutive securities
Antidilutive securities (in shares)	7,492,970	10,045,155
Nonvested restricted stock units issued and outstanding
Anti-dilutive securities
Antidilutive securities (in shares)	8,039,823	8,813,737
Class A common stock reserved for Twilio.org
Anti-dilutive securities
Antidilutive securities (in shares)	773,571	776,334
Class A common stock committed under 2016 ESPP
Anti-dilutive securities
Antidilutive securities (in shares)	212,028	113,959
Conversion spread
Anti-dilutive securities
Antidilutive securities (in shares)	2,747,996	2,873,836
Unvested shares subject to repurchase
Anti-dilutive securities
Antidilutive securities (in shares)	0	1,250