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Debt - Additional Information (Details) $ / shares in Units, € in Millions			1 Months Ended	12 Months Ended
	Jun. 01, 2016 USD ($)	Jun. 17, 2014 USD ($)	Jan. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) Loan $ / shares	Apr. 30, 2017 USD ($)	Apr. 30, 2017 EUR (€)	Mar. 31, 2017 USD ($)	Mar. 31, 2017 EUR (€)	Dec. 31, 2016 USD ($)	Apr. 18, 2016 USD ($)	Apr. 18, 2016 EUR (€)
Research and development loans
Debt Instrument [Line Items]
Principal				$ 2,600,000
Fair value of debt										$ 2,900,000	€ 2.6
Finland's Ministry of Finance \| Research and development loans
Debt Instrument [Line Items]
Basis Spread to be reduced (as a percent)				3.00%
Loan repayment beginning period				2017-01
Period in which equal annual installments to be paid				5 years
Loan repayment ending period				2021-01
Minimum \| Finland's Ministry of Finance \| Research and development loans
Debt Instrument [Line Items]
Effective interest rate on liability component (as a percent)				1.00%
Letters of Credit
Debt Instrument [Line Items]
Restricted Cash and Cash Equivalents				$ 600,000
JPMorgan Chase Bank, N.A. \| Senior secured revolving credit facility
Debt Instrument [Line Items]
Term of debt	3 years
Maximum borrowing capacity	$ 60,000,000
Debt issuance costs written off				1,100,000
Saints Capital Notes
Debt Instrument [Line Items]
Convertible notes paid			$ 800,000
Notes
Debt Instrument [Line Items]
Interest rate (as a percent)		1.75%
Net proceeds from offering, after deducting Underwriter's discount and estimated offering expenses payable		$ 337,500,000
Principal		$ 345,000,000		$ 345,000,000					$ 345,000,000
Notes maturity date				Jun. 15, 2021
Notes frequency of periodic payment				semiannually in arrears in cash
Period to comply with covenants				270 days
Debt issuance costs				$ 7,500,000
Debt issuance costs allocated to equity component				1,300,000
Debt issuance costs allocated to liability component				$ 6,200,000
Term of debt				7 years
Debt fair value amount				$ 296,000,000
Remaining contractual life				3 years 6 months
Effective interest rate on liability component (as a percent)				4.80%
Notes \| Debt Conversion Terms upon Occurrence of Certain Fundamental Company Changes
Debt Instrument [Line Items]
Principal amount of Notes or an integral multiple thereof in which holder may repurchase the Notes				$ 1,000,000
Notes \| Debt Conversion Event Term
Debt Instrument [Line Items]
Minimum percentage of aggregate principal amount held by bondholders to declare notes due and payable				25.00%
In event of default arising out of certain bankruptcy events, percentage of principal amount due and payable				100.00%
Notes \| Convertible Debt Holder
Debt Instrument [Line Items]
Initial conversion rate of common stock				23.4968
Initial conversion price of convertible notes into common stock (in dollars per share) \| $ / shares				$ 42.56
Non-Convertible Capital Loan
Debt Instrument [Line Items]
Principal				$ 23,700,000
Fair value of debt										$ 23,300,000	€ 20.6
Number of loans \| Loan				14
Non-Convertible Capital Loan \| Finland's Ministry of Finance
Debt Instrument [Line Items]
Basis Spread to be reduced (as a percent)				1.00%
Non-Convertible Capital Loan \| Minimum
Debt Instrument [Line Items]
Term of debt				8 years
Non-Convertible Capital Loan \| Minimum \| Finland's Ministry of Finance
Debt Instrument [Line Items]
Effective interest rate on liability component (as a percent)				3.00%
Non-Convertible Capital Loan \| Maximum
Debt Instrument [Line Items]
Term of debt				10 years
Convertible Capital Loans
Debt Instrument [Line Items]
Repurchased outstanding principal amount				$ 0	$ 200,000	€ 0.2	$ 1,700,000	€ 1.5