Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 03, 2019	Mar. 31, 2019	Aug. 09, 2018	Feb. 03, 2016	Nov. 02, 2015
Operating Loss Carryforwards [Line Items]
Deferred tax assets, valuation allowance	$ 139,855	$ 135,216
Change in valuation allowance	4,600
Net change in valuation allowance, recorded as tax expense	2,899	16,360	$ (24,976)
Undistributed earnings of foreign subsidiaries	100
Income tax (benefit) expense	$ (4,725)	$ 284	$ (459)
Effective tax rate	(6.80%)
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, state and local	$ 217,100
State and Local Jurisdiction | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Tax credit carryforward amount	15,900
State and Local Jurisdiction | TriVascular Technologies, Inc.
Operating Loss Carryforwards [Line Items]
Decrease in net operating loss carryforwards							$ 209,400
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, domestic	350,800
Federal alternative minimum tax credit carryforwards	100
Internal Revenue Service (IRS) | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Tax credit carryforward amount	10,200
Internal Revenue Service (IRS) | TriVascular Technologies, Inc.
Operating Loss Carryforwards [Line Items]
Decrease in net operating loss carryforwards							230,300
Internal Revenue Service (IRS) | TriVascular Technologies, Inc. | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Decrease in research and development credits							$ 3,100
Income Tax Expense (Benefit)
Operating Loss Carryforwards [Line Items]
Net change in valuation allowance, recorded as tax expense	2,900
Income Tax Expense (Benefit) | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net change in valuation allowance, recorded as tax expense	1,700
Convertible notes
Operating Loss Carryforwards [Line Items]
Income tax (benefit) expense	$ 5,000
Convertible Senior Notes Due 2020
Operating Loss Carryforwards [Line Items]
Debt instrument, stated interest rate	3.25%					3.25%
Convertible Senior Notes Due 2020 | Convertible notes
Operating Loss Carryforwards [Line Items]
Debt instrument, stated interest rate						3.25%		3.25%
5% Note | Convertible notes
Operating Loss Carryforwards [Line Items]
Debt instrument, stated interest rate				5.00%	5.00%