Credit Facilities (Details)								1 Months Ended	3 Months Ended
	Apr. 03, 2017 USD ($)	Jul. 29, 2016 USD ($)	Jun. 02, 2016 USD ($) shares	Feb. 03, 2016 shares	Nov. 02, 2015 USD ($) $ / shares	Jul. 21, 2015 USD ($)	Dec. 10, 2013 USD ($) $ / shares $ / security	Feb. 29, 2016 USD ($)	Mar. 31, 2017 USD ($) d $ / shares shares	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) shares	Jun. 01, 2016 shares	Dec. 31, 2015 USD ($)	Nov. 30, 2015 USD ($)
Line of Credit Facility [Line Items]
Convertible notes									$ 179,669,000		$ 177,178,000
Payments of derivative issuance costs							$ 7,400,000
Common stock authorized (in shares) | shares			135,000,000						135,000,000		135,000,000	100,000,000
Adjustments to additional paid-in capital, conversion features of Senior Notes			$ 68,600,000
Change in fair value of derivative liabilities									$ 0	$ (5,088,000)
Restricted cash									$ 2,000,000
Revolving Credit Facility | Bank of America
Line of Credit Facility [Line Items]
Aggregate maximum borrowing capacity						$ 20,000,000
Minimum current ratio									1.5
Revolving Credit Facility | MidCap
Line of Credit Facility [Line Items]
Debt issuance costs, net									$ (800,000)
Aggregate maximum borrowing capacity		$ 50,000,000.0
Maximum amount on which fees are calculated		$ 10,000,000
Unused line fee		0.50%
Collateral management fee		0.50%
Deferred financing costs									900,000
Amount outstanding									$ 0
Revolving Credit Facility | MidCap | Subsequent Event
Line of Credit Facility [Line Items]
Debt termination fees	$ 2,600,000
Revolving Credit Facility | MidCap | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate		4.10%							5.00%
Variable rate, maximum		0.50%
Letter of Credit | Bank of America
Line of Credit Facility [Line Items]
Aggregate maximum borrowing capacity						$ 10,000,000
Term of line of credit						2 years
Termination notice period									3 days
TriVascular Technologies, Inc.
Line of Credit Facility [Line Items]
Equity consideration issued in merger (in shares) | shares				13,586,503
Minimum | Revolving Credit Facility | Bank of America
Line of Credit Facility [Line Items]
Liquidation proceeds, monetary amount									$ 30,000,000
Other Assets | Accounting Standards Update 2015-03 | Revolving Credit Facility | MidCap
Line of Credit Facility [Line Items]
Debt issuance costs, net									900,000
Long-term Debt | Accounting Standards Update 2015-03 | Revolving Credit Facility | MidCap
Line of Credit Facility [Line Items]
Debt issuance costs, net									$ (900,000)
3.25% Convertible Senior Notes | Other Assets | Accounting Standards Update 2015-03
Line of Credit Facility [Line Items]
Debt issuance costs, net													$ 2,900,000
Convertible Debt
Line of Credit Facility [Line Items]
Reclassification of conversion features to derivative liabilities								$ 24,800,000
Convertible Debt | 2.25% Convertible Senior Notes
Line of Credit Facility [Line Items]
Debt instrument face amount							86,250,000
Stated interest rate									2.25%
Proceeds from convertible debt							$ 82,600,000
Redemption price percentage									100.00%
Conversion of convertible securities									41.6051
Convertible conversion price (in dollars per share) | $ / shares							$ 24.04		$ 24.04
Violation or event of default, declaration by note holders, percentage									25.00%
Fair value disclosure							$ 66,900,000
Beneficial conversion feature							19,300,000
Unamortized discount							3,700,000
Convertible notes							$ 86,300,000		$ 78,800,000
Deferred finance costs, noncurrent, net									1,200,000
Periodic principal payment									0
Cap price (in dollars per security) | $ / security							29.02
Convertible Debt | 2.25% Convertible Senior Notes | Minimum
Line of Credit Facility [Line Items]
Periodic interest payment									5,700,000
Convertible Debt | 2.25% Convertible Senior Notes | Maximum
Line of Credit Facility [Line Items]
Periodic interest payment									$ 6,900,000
Convertible Debt | 2.25% Convertible Senior Notes | Other Assets
Line of Credit Facility [Line Items]
Unamortized discount							$ 2,900,000
Convertible Debt | 2.25% Convertible Senior Notes | Other Assets | Accounting Standards Update 2015-03
Line of Credit Facility [Line Items]
Debt issuance costs, net													1,900,000
Convertible Debt | 2.25% Convertible Senior Notes | Additional Paid-in Capital
Line of Credit Facility [Line Items]
Unamortized discount							$ 800,000
Convertible Debt | 2.25% Convertible Senior Notes | Long-term Debt | Accounting Standards Update 2015-03
Line of Credit Facility [Line Items]
Debt issuance costs, net													(1,900,000)
Convertible Debt | 2.25% Convertible Senior Notes | Redemption, Period One
Line of Credit Facility [Line Items]
Threshold trading days | d									20
Threshold consecutive trading days									30 days
Threshold percentage of stock price trigger									130.00%
Redemption price percentage									100.00%
Convertible Debt | 2.25% Convertible Senior Notes | Redemption, Period Two
Line of Credit Facility [Line Items]
Threshold trading days | d									20
Threshold consecutive trading days									5 years
Threshold percentage of stock price trigger									98.00%
Threshold consecutive business days									30 days
Threshold business days | d									5
Convertible Debt | 3.25% Convertible Senior Notes
Line of Credit Facility [Line Items]
Debt instrument face amount					$ 125,000,000.0
Stated interest rate									3.25%
Threshold consecutive trading days									30 days
Redemption price percentage									100.00%
Conversion of convertible securities					89.4314
Convertible conversion price (in dollars per share) | $ / shares					$ 11.18
Holding threshold required to declare debt due									25.00%
Fair value disclosure					$ 97,800,000
Beneficial conversion feature					27,200,000
Unamortized discount					2,900,000
Convertible notes									$ 104,300,000					$ 125,000,000
Deferred finance costs, noncurrent, net									2,200,000
Periodic principal payment									$ 0
Convertible Debt | 3.25% Convertible Senior Notes | Convertible Condition One
Line of Credit Facility [Line Items]
Threshold trading days | d									20
Threshold consecutive trading days									30 days
Threshold percentage of stock price trigger									130.00%
Convertible Debt | 3.25% Convertible Senior Notes | Convertible Condition Two
Line of Credit Facility [Line Items]
Threshold percentage of stock price trigger									98.00%
Threshold consecutive business days									5 days
Threshold business days | d									5
Convertible Debt | 3.25% Convertible Senior Notes | Convertible Condition Three
Line of Credit Facility [Line Items]
Threshold trading days | d									2
Convertible Debt | 3.25% Convertible Senior Notes | Minimum
Line of Credit Facility [Line Items]
Periodic interest payment									$ 9,100,000
Convertible Debt | 3.25% Convertible Senior Notes | Maximum
Line of Credit Facility [Line Items]
Periodic interest payment									$ 10,700,000
Convertible Debt | 3.25% Convertible Senior Notes | Other Assets
Line of Credit Facility [Line Items]
Unamortized discount					3,700,000
Convertible Debt | 3.25% Convertible Senior Notes | Additional Paid-in Capital
Line of Credit Facility [Line Items]
Unamortized discount					$ 800,000
Convertible Debt | 3.25% Convertible Senior Notes | Long-term Debt | Accounting Standards Update 2015-03
Line of Credit Facility [Line Items]
Debt issuance costs, net													$ (2,900,000)
Convertible Debt | 3.25% Convertible Senior Notes | Redemption, Period One
Line of Credit Facility [Line Items]
Threshold trading days | d									30
Convertible Debt | 3.25% Convertible Senior Notes | Redemption, Period Two
Line of Credit Facility [Line Items]
Threshold trading days | d									2