Schedule of Cash as Reported in Condensed Consolidated Statements of Cash Flows (Detail) - USD ($)	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Restricted Cash And Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 226,793,000	$ 138,951,000
Restricted cash	1,528,000	1,062,000
Total cash balance in condensed consolidated statements of cash flows	228,321,000	140,013,000	$ 168,461,000	$ 181,741,000
SRX Cardio
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash	29,000	30,000
Royalty Payments | HealthCare Royalty Partners and its Affiliates (“HCR”)
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash	$ 1,499,000	$ 1,032,000