Credit Facilities (3.25% Convertible Senior Notes due 2020) (Details)				1 Months Ended		12 Months Ended
	Jun. 02, 2016 USD ($) shares	Nov. 02, 2015 USD ($) $ / shares	Dec. 10, 2013 USD ($) $ / shares	Feb. 29, 2016 USD ($)	Feb. 23, 2016 shares	Dec. 31, 2017 USD ($) d shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Jun. 01, 2016 shares
Debt Instrument [Line Items]
Debt						$ 208,253,000	$ 177,178,000
Common stock, authorized (in shares) | shares	135,000,000					135,000,000	100,000,000		100,000,000
Adjustment to additional paid-in capital, conversion of Senior Notes	$ 68,600,000
Change in fair value of derivative liabilities						$ 0	$ 43,831,000	$ 0
TriVascular Technologies, Inc.
Debt Instrument [Line Items]
Shares issued in connection with acquisition (in shares) | shares					13,600,000
Convertible Senior Notes
Debt Instrument [Line Items]
Reclassification of conversion features to derivative liabilities				$ 24,800,000
Convertible Senior Notes | 3.25% Convertible Senior Notes
Debt Instrument [Line Items]
Convertible notes, face amount		$ 125,000,000.0
Convertible notes, stated percentage		3.25%
Convertible debt redemption, trading days threshold | d						20
Convertible debt redemption, consecutive trading days threshold | d						30
Convertible debt redemption, percentage of stock price trigger, percentage						130.00%
Debt instrument, redemption price, percentage		98.00%				100.00%
Convertible debt redemption, consecutive business days threshold						5 days
Convertible debt redemption, business days threshold | d						5
Convertible debt, conversion ratio		0.0894314
Convertible debt, conversion price (in dollars per share) | $ / shares		$ 11.18
Debt instrument, fair value		$ 97,800,000
Debt instrument, embedded conversion option						$ 27,200,000
Unamortized debt discount		3,700,000
Debt						108,100,000
Deferred financing costs						1,800,000
Convertible Senior Notes | 3.25% Convertible Senior Notes | Minimum
Debt Instrument [Line Items]
Estimated annual interest expense, debt						9,100,000
Convertible Senior Notes | 3.25% Convertible Senior Notes | Maximum
Debt Instrument [Line Items]
Estimated annual interest expense, debt						10,700,000
Convertible Senior Notes | 3.25% Convertible Senior Notes | Other Assets
Debt Instrument [Line Items]
Unamortized debt discount		2,900,000
Convertible Senior Notes | 3.25% Convertible Senior Notes | Other Assets | Accounting Standards Update 2015-03
Debt Instrument [Line Items]
Debt issuance costs							(2,900,000)
Convertible Senior Notes | 3.25% Convertible Senior Notes | Additional Paid-In Capital
Debt Instrument [Line Items]
Unamortized debt discount		$ 800,000
Convertible Senior Notes | 3.25% Convertible Senior Notes | Long-term Debt | Accounting Standards Update 2015-03
Debt Instrument [Line Items]
Debt issuance costs							2,900,000
Convertible Senior Notes | 2.25% Convertible Senior Notes
Debt Instrument [Line Items]
Convertible notes, face amount			$ 86,250,000
Convertible notes, stated percentage			2.25%
Debt instrument, redemption price, percentage			100.00%
Convertible debt, conversion ratio			0.0416051
Convertible debt, conversion price (in dollars per share) | $ / shares			$ 24.04
Debt instrument, fair value			$ 66,900,000
Debt instrument, embedded conversion option			19,300,000
Unamortized debt discount			3,700,000
Debt issuance costs						200,000
Debt						$ 17,400,000
Convertible Senior Notes | 2.25% Convertible Senior Notes | Other Assets
Debt Instrument [Line Items]
Unamortized debt discount			2,900,000
Convertible Senior Notes | 2.25% Convertible Senior Notes | Other Assets | Accounting Standards Update 2015-03
Debt Instrument [Line Items]
Debt issuance costs							(1,900,000)
Convertible Senior Notes | 2.25% Convertible Senior Notes | Additional Paid-In Capital
Debt Instrument [Line Items]
Unamortized debt discount			$ 800,000
Convertible Senior Notes | 2.25% Convertible Senior Notes | Long-term Debt | Accounting Standards Update 2015-03
Debt Instrument [Line Items]
Debt issuance costs							$ 1,900,000