Commitments and Contingencies - Additional Information (Detail)	1 Months Ended	3 Months Ended	12 Months Ended				49 Months Ended
	Nov. 30, 2017 USD ($) ft²	Jun. 30, 2018 USD ($)	Sep. 30, 2018 USD ($) € / $ shares	Sep. 30, 2018 EUR (€) shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2023 USD ($)
Commitments And Contingencies [Line Items]
Additional shares of common stock to stockholders | shares			480,059	480,059
License agreement commencement date			2006-03	2006-03
Annual minimum payments for licenses			$ 13,997,000		$ 11,422,000	$ 10,908,000
Exchange rate relating to license payment | € / $			1.1602
Future minimum payments associated with license			$ 2,100,000
Rent expense related to operating leases			500,000		100,000	$ 100,000
Acquired in-process research and development			7,888,000
Other long-term liabilities			5,720,000		$ 1,938,000
Eden Prairie Minnesota [Member]
Commitments And Contingencies [Line Items]
Square feet of office and R&D facility | ft²	36,000
Contractual obligations	$ 4,000,000
Operating lease agreement term	10 years
Operating lease agreement commencement date	2018-05
CRO [Member]
Commitments And Contingencies [Line Items]
Contractual obligation to be paid			13,200,000
Minimum [Member] | CRO [Member]
Commitments And Contingencies [Line Items]
Contractual obligation due in next several years			32,000,000
Maximum [Member] | CRO [Member]
Commitments And Contingencies [Line Items]
Contractual obligations			20,000,000
Contractual obligation due in next several years			40,000,000
License [Member]
Commitments And Contingencies [Line Items]
Annual minimum payments for licenses			$ 232,000	€ 200,000
Patents [Member]
Commitments And Contingencies [Line Items]
Patent expiry date			2027-09	2027-09
Intellectual Property [Member] | Embolitech LLC [Member]
Commitments And Contingencies [Line Items]
Payments to acquire intellectual property assets		$ 7,900,000	$ 5,000,000
Contingent payments upon achievement of regulatory milestones			2,000,000
Acquired in-process research and development			7,900,000
Other long-term liabilities			2,900,000
Intellectual Property [Member] | Embolitech LLC [Member] | Scenario Forecast [Member]
Commitments And Contingencies [Line Items]
Estimated additional payment to acquire intellectual property assets							$ 3,500,000
Selling, general and administrative [Member]
Commitments And Contingencies [Line Items]
Claim accrual recorded in selling, general and other administrative expenses			1,000,000
Other Accrued Liabilities [Member]
Commitments And Contingencies [Line Items]
Claim accrual recorded in other accrued liabilities			$ 1,000,000