Summary of Significant Accounting Policies and Select Balance Sheet Information - Additional Information (Detail) - USD ($) shares in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Oct. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
AFS investments net unrealized loss reclassified out of accumulated other comprehensive income (loss) with a corresponding adjustment to other income (loss)									$ 0	$ 0	$ 0
Held-to-maturity debt securities	$ 0				$ 0				0	0
Realized gains or losses on sales of available-for-sale securities									0	0	0
Depreciation expense									4,800,000	4,700,000	3,700,000
Amortization expense									2,500,000	2,600,000	2,700,000
Impairment loss									0		0
Goodwill impairment charges									0	0	0
Impairment charges relating to long-lived assets									0	0	0
Revenue	22,543,000	$ 26,883,000	$ 22,822,000	$ 22,616,000	30,816,000	$ 24,344,000	$ 22,676,000	$ 22,241,000	94,864,000	100,077,000	81,336,000
Income tax (benefit) provision									$ (2,577,000)	$ (34,000)	$ (3,075,000)
Antidilutive options excluded from computation of EPS									0.1	0.2	1.0
ASC Topic 842 adoption, right-of-use asset	2,508,000								$ 2,508,000
ASC Topic 842 adoption, lease liability	3,776,000								3,776,000
Deferred rent liability	1,200,000								1,200,000
Abbott Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Revenue									12,000,000.0	$ 13,500,000	$ 4,400,000
Collaborative arrangement payment received									45,800,000
Collaborative arrangement additional potential milestone payments receivable	45,000,000								45,000,000
Abbott Agreement [Member] | Upfront Payment [Member]
Summary Of Significant Accounting Policies [Line Items]
Collaborative arrangement payment received											25,000,000
Abbott Agreement [Member] | Milestone Payment [Member]
Summary Of Significant Accounting Policies [Line Items]
Collaborative arrangement payment received		$ 10,800,000			10,000,000				$ 10,800,000	10,000,000
Abbott Agreement [Member] | TRANSCEND Clinical Trial [Member]
Summary Of Significant Accounting Policies [Line Items]
Clinical study completion period									5 years
Abbott Agreement [Member] | Clinical Trial Report Milestone [Member] | TRANSCEND Clinical Trial [Member]
Summary Of Significant Accounting Policies [Line Items]
Collaborative arrangement additional potential milestone payments receivable	15,000,000								$ 15,000,000
Abbott Agreement [Member] | PMA Milestone [Member] | TRANSCEND Clinical Trial [Member]
Summary Of Significant Accounting Policies [Line Items]
Collaborative arrangement additional potential milestone payments receivable	$ 30,000,000								30,000,000
IDA [Member]
Summary Of Significant Accounting Policies [Line Items]
Reimbursement recorded as reduction to R&D expense									$ 800,000	$ 700,000	$ 800,000
Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Performance obligations, payment terms, royalties									45 days
Revenue [Member] | Customer Concentration Risk [Member] | Abbott [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of consolidated revenue									19.00%	19.00%	11.00%
Revenue [Member] | Customer Concentration Risk [Member] | Medtronic [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of consolidated revenue									14.00%	14.00%	16.00%
Revenue [Member] | Product Concentration Risk | Abbott Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of consolidated revenue									13.00%	13.00%	5.00%
ASC Topic 842 [Member]
Summary Of Significant Accounting Policies [Line Items]
ASC Topic 842 adoption, right-of-use asset												$ 1,700,000
ASC Topic 842 adoption, lease liability												$ 2,900,000
Impact of Adoption [Member] | Adoption of ASC Topic 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Revenue										$ 1,300,000
Income tax (benefit) provision										300,000
Leases [Member]
Summary Of Significant Accounting Policies [Line Items]
Lease description									The Company leases facilities for research, office, manufacturing and warehousing.
Lease, existence of option to extend									true
Lease, option to extend									The Company’s leases include one or more options to renew and extend the lease term at the Company’s discretion. These renewal options are not included in right-of-use assets and lease liabilities as they are not reasonably certain of exercise.
Operating lease cost									$ 600,000
Rent expense related to operating leases										500,000	$ 500,000
Weighted average remaining lease term for operating leases	7 years 3 months 18 days								7 years 3 months 18 days
Weighted average discount rate used to determine operating lease liabilities	4.00%								4.00%
Research and development expense [Member] | In-Process Research and Development [Member]
Summary Of Significant Accounting Policies [Line Items]
Impairment loss										300,000
ViaCyte, Inc. [Member]
Summary Of Significant Accounting Policies [Line Items]
Original cost of investment	$ 5,300,000								$ 5,300,000
Other-than-temporary impairment loss on investment			$ 500,000						500,000	4,800,000
Carrying amount of investment	$ 0				$ 500,000				$ 0	$ 500,000
Maximum [Member] | Revenue [Member] | Customer Concentration Risk [Member] | Medtronic [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of consolidated revenue									5.00%
Maximum [Member] | Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Performance obligations, payment terms, product sales									45 days
Performance obligations, payment terms, R&D services									45 days
Maximum [Member] | ViaCyte, Inc. [Member]
Summary Of Significant Accounting Policies [Line Items]
Company's ownership percentage	1.00%								1.00%
Minimum [Member] | Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Performance obligations, payment terms, product sales									30 days
Performance obligations, payment terms, R&D services									30 days