Quarterly Financial Data (Unaudited) - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended								9 Months Ended	12 Months Ended
	Aug. 31, 2019	Dec. 31, 2017	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Quarterly Financial Data [Line Items]
Discrete tax expense										$ 1,200			$ 1,600
U.S. federal statutory tax rate		21.00%								35.00%		21.00%	24.50%	35.00%
Total revenue			$ 30,816	$ 24,344	$ 22,676	$ 22,241	$ 23,038	$ 22,227	$ 19,058	$ 17,013		$ 100,077	$ 81,336	$ 73,112
Intellectual Property [Member]
Quarterly Financial Data [Line Items]
Payments to acquire intellectual property assets			900
Embolitech LLC [Member] | Intellectual Property [Member]
Quarterly Financial Data [Line Items]
Payments to acquire intellectual property assets								$ 7,900				5,000
Abbott [Member] | Clinical [Member]
Quarterly Financial Data [Line Items]
Recognized Revenue			$ 5,100
Milestone payment received	$ 10,000
Royalties and License Fees [Member]
Quarterly Financial Data [Line Items]
Total revenue				$ 1,000								$ 48,458	$ 35,424	$ 31,787
Royalties and License Fees [Member] | Abbott [Member]
Quarterly Financial Data [Line Items]
Total revenue											$ 4,400