TriVascular Merger (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
	Feb. 03, 2016	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Share price (in dollars per share)	$ 7.42
Net sales		$ 44,003	$ 45,986	$ 48,556	$ 42,612	$ 47,463	$ 52,122	$ 50,974	$ 42,366	$ 181,157	$ 192,925	$ 153,612
TriVascular Technologies, Inc.
Business Acquisition [Line Items]
Equity consideration issued in merger (in shares)	13,586,503
Equity consideration issued in merger	$ 100,800
Revision of net assets acquired and goodwill										27,100
Adjustment to accounts receivable, increase										200
Adjustment to accrued liabilities and other, increase										600
Adjustment to inventories, increase (decrease)										200
Adjustment to prepaid expenses and other current assets, increase										100
Adjustment to intangible assets, decrease										$ 27,000
Adjustment to amortization of intangibles, decrease				(300)
Gross contractual trade receivables	5,800
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
TriVascular Technologies, Inc. | Cost of goods sold
Business Acquisition [Line Items]
Adjustment to amortization of intangibles, decrease				(200)
TriVascular Technologies, Inc. | Marketing and sales
Business Acquisition [Line Items]
Adjustment to amortization of intangibles, decrease				$ (49)