Stock-based compensation expense - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022
Shares
Beginning balance (in shares)	2,453,000
Granted (in shares)	0
Forfeited (in shares)	(37,000)
Exercised (in shares)	(35,000)
Ending balance (in shares)	2,381,000	2,453,000
Number of options, Nonvested at December 31, 2022 (in shares)	427,000
Number of options, Exercisable (in shares)	1,954,000
Weighted average exercise price per share
Beginning balance (in usd per share)	$ 24.67
Granted (in usd per share)	0
Forfeited (in usd per share)	42.87
Exercised (in dollars per share)	17.17
Ending balance (in usd per share)	24.49	$ 24.67
Weighted average exercise price per share, Nonvested at December 31, 2022 (in dollars per share)	33.87
Vested and exercisable (in usd per share)	$ 22.44
Weighted average remaining contractual term (years)
Outstanding	6 years 21 days	6 years 3 months 29 days
Weighted average remaining contractual term (years), Nonvested at December 31, 2022	6 years 11 months 1 day
Weighted average remaining contractual term (years), Exercisable	5 years 10 months 13 days
Aggregate Intrinsic Value
Aggregate intrinsic value, outstanding beginning balance	$ 33,447
Exercised	312
Aggregate intrinsic value, outstanding ending balance	10,715	$ 33,447
Aggregate intrinsic value, nonvested	423
Aggregate intrinsic value, Vested and exercisable	$ 10,292
Performance Stock Options
Shares
Beginning balance (in shares)	312,000
Vested (in shares)	(237,000)
Ending balance (in shares)	312,000	312,000
Number of options, Nonvested at December 31, 2022 (in shares)	56,000	293,000
Number of options, Exercisable (in shares)	256,000	19,000
Weighted average exercise price per share
Beginning balance (in usd per share)	$ 61.35
Vested (in usd per share)	70.84
Ending balance (in usd per share)	61.35	$ 61.35
Weighted average exercise price per share, Nonvested at December 31, 2022 (in dollars per share)	31.29	63.27
Vested and exercisable (in usd per share)	$ 67.95	$ 31.29
Weighted average remaining contractual term (years)
Outstanding	8 years 29 days	8 years 3 months 29 days
Weighted average remaining contractual term (years), Nonvested at December 31, 2022	9 years 3 months 25 days	8 years 3 months
Weighted average remaining contractual term (years), Exercisable	7 years 9 months 21 days	9 years 6 months 25 days
Aggregate Intrinsic Value
Aggregate intrinsic value, outstanding beginning balance	$ 296
Aggregate intrinsic value, outstanding ending balance		$ 296
Aggregate intrinsic value, nonvested		222
Aggregate intrinsic value, Vested and exercisable		$ 74