Net income per share - Reconciliation of Numerator and Denominator in Basic and Diluted Net Income (Loss) Per Common Share Computations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income	$ 447	$ 1,512	$ 6,517	$ 3,706	$ 1,959	$ 10,223
Denominator:
Weighted average common shares outstanding - basic (in shares)	49,147,366		48,419,845		49,036,519	48,383,095
Dilutive common equivalent shares from equity awards (in shares)	2,601,071		2,520,070		2,308,278	2,245,609
Weighted average common shares outstanding - diluted (in shares)	51,748,437		50,939,915		51,344,797	50,628,704
Net income per share:
Basic (in USD per share)	$ 0.01		$ 0.13		$ 0.04	$ 0.21
Diluted (in USD per share)	$ 0.01		$ 0.13		$ 0.04	$ 0.20
Anti-dilutive securities excluded from diluted EPS:
Weighted average anti-dilutive shares from outstanding equity awards excluded from diluted earnings per share (in shares)	857,698		1,944,662		1,712,824	2,417,982