Revenues - Disaggregation of Revenue (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Disaggregation of Revenue [Line Items]
Revenues		$ 145,263	$ 139,502	$ 134,201	$ 128,439	$ 120,793	$ 111,806	$ 109,638	$ 102,701	$ 547,405	$ 444,938	$ 333,764
Cumulative effect adjustments													$ 467
Neuro
Disaggregation of Revenue [Line Items]
Revenues										331,685	294,333	232,446
Vascular
Disaggregation of Revenue [Line Items]
Revenues										215,720	150,605	101,318
United States
Disaggregation of Revenue [Line Items]
Revenues										355,222	290,716	219,173
Japan
Disaggregation of Revenue [Line Items]
Revenues										42,520	41,805	33,790
Other International
Disaggregation of Revenue [Line Items]
Revenues										$ 149,663	$ 112,417	$ 80,801
Retained Earnings (Accumulated Deficit)
Disaggregation of Revenue [Line Items]
Cumulative effect adjustments	[1]												467
Retained Earnings (Accumulated Deficit) | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Cumulative effect adjustments													$ 300

[1] Cumulative effect adjustments relate to the adoption of Accounting Standard Update (“ASU”) No. 2014-09 - Revenue from Contracts with Customers (“Topic 606”), ASU No. 2016-16 - Income Taxes (“Topic 740”), and ASU No. 2018-02 - Income Statement - Reporting Comprehensive Income (“Topic 220”). Refer to the accompanying notes, including Note “2. Summary of Significant Accounting Policies,” for more information.