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TriVascular Merger - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 03, 2016	Dec. 31, 2018
Business Acquisition [Line Items]
Share price (in dollars per share)		$ 7.16
TriVascular Technologies, Inc.
Business Acquisition [Line Items]
Intangible assets	$ 46,200
TriVascular Technologies, Inc. \| In-process research and development
Business Acquisition [Line Items]
Intangible assets	11,200
TriVascular Technologies, Inc. \| Customer relationships
Business Acquisition [Line Items]
Intangible assets	$ 7,500
Acquired intangible assets, useful life	10 years
TriVascular Technologies, Inc. \| Developed technology
Business Acquisition [Line Items]
Intangible assets	$ 27,500
Acquired intangible assets, useful life	11 years
Common Stock
Business Acquisition [Line Items]
Equity consideration issued in merger	$ 100,800
Share price (in dollars per share)	$ 74.2
Common Stock \| TriVascular Technologies, Inc.
Business Acquisition [Line Items]
Equity consideration issued in merger (in shares)	1,358,650