Cash, cash equivalents and short-term investments - Summary of Fair Value and Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Fair Value
Less than 12 Months	$ 5,093
12 Months or Greater	22,142
Total	27,235
Unrealized Losses
Less than 12 Months	(4)
12 Months or Greater	(41)
Total	(45)
U.S. treasury securities
Fair Value
Less than 12 Months	0
12 Months or Greater	2,992
Total	2,992
Unrealized Losses
Less than 12 Months	0
12 Months or Greater	(5)
Total	(5)
U.S. agency securities
Fair Value
Less than 12 Months	0
12 Months or Greater	998
Total	998
Unrealized Losses
Less than 12 Months	0
12 Months or Greater	(1)
Total	(1)
Asset-backed securities
Fair Value
Less than 12 Months	0
12 Months or Greater	3,537
Total	3,537
Unrealized Losses
Less than 12 Months	0
12 Months or Greater	(11)
Total	(11)
Municipal securities
Fair Value
Less than 12 Months	0
12 Months or Greater	0
Total	0
Unrealized Losses
Less than 12 Months	0
12 Months or Greater	0
Total	0
Commercial paper
Fair Value
Less than 12 Months	493
12 Months or Greater	0
Total	493
Unrealized Losses
Less than 12 Months	(1)
12 Months or Greater	0
Total	(1)
Corporate bonds
Fair Value
Less than 12 Months	4,600
12 Months or Greater	14,615
Total	19,215
Unrealized Losses
Less than 12 Months	(3)
12 Months or Greater	(24)
Total	$ (27)