Credit Facilities (Details)						3 Months Ended			6 Months Ended
	Jan. 05, 2018 USD ($)	Apr. 03, 2017 USD ($) $ / shares shares	Jul. 29, 2016 USD ($)	Nov. 02, 2015 USD ($) $ / shares	Dec. 10, 2013 USD ($) $ / shares $ / security	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) d $ / shares shares	Jun. 30, 2017 USD ($)	Dec. 31, 2017 shares	Nov. 30, 2015 USD ($)
Line of Credit Facility [Line Items]
Loss on debt extinguishment						$ 0		$ (6,512,000)	$ (2,270,000)	$ (6,512,000)
Payments of derivative issuance costs					$ 7,400,000
Common stock authorized (in shares) | shares						170,000,000			170,000,000		135,000,000
Debt termination fees									$ 1,310,000	$ 2,515,000
Revolving Credit Facility | MidCap
Line of Credit Facility [Line Items]
Aggregate maximum borrowing capacity			$ 50,000,000.0
Restricted cash						$ 2,000,000			2,000,000
Write off of deferred financing costs							$ 800,000
Debt termination fees							$ 2,500,000
Revolving Credit Facility | MidCap | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate			4.10%
Variable rate, maximum			0.50%
Revolving Credit Facility | Deerfield Revolver
Line of Credit Facility [Line Items]
Loss on debt extinguishment	$ (2,300,000)
Debt issuance costs		$ 1,200,000
Aggregate maximum borrowing capacity		$ 50,000,000
Restricted cash						2,000,000			2,000,000
Write off of deferred financing costs	1,000,000
Debt termination fees	$ 1,300,000
Revolving Credit Facility | Deerfield Revolver | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate		4.60%
Variable rate, floor		1.00%
Other Assets | Accounting Standards Update 2015-03 | Revolving Credit Facility | MidCap
Line of Credit Facility [Line Items]
Debt issuance costs, net						(900,000)			$ (900,000)
Facility Agreement | Deerfield Warrants
Line of Credit Facility [Line Items]
Expiration date of warrants issued									7 years
Warrant exercise limitation threshold									4.985%
Facility Agreement | Common Stock | Deerfield Warrants
Line of Credit Facility [Line Items]
Debt issuance costs		$ 400,000
Shares in which warrants can be converted (in shares) | shares		6,470,000
Exercise price of warrants issued (in dollars per share) | $ / shares		$ 9.23
Fair value of warrants		$ 14,300,000
3.25% Convertible Senior Notes
Line of Credit Facility [Line Items]
Debt instrument face amount						$ 40,500,000			$ 40,500,000
Stated interest rate						3.25%			3.25%
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%	2.25%			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			$ 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
Repurchased debt amount		68,000,000
Beneficial conversion feature adjustment		(2,200,000)
Loss on debt extinguishment		(3,200,000)
Convertible notes					$ 86,300,000	$ 17,800,000			$ 17,800,000
Deferred finance costs, noncurrent, net						100,000			100,000
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									1,100,000
Convertible Debt | 2.25% Convertible Senior Notes | Maximum
Line of Credit Facility [Line Items]
Periodic interest payment									$ 1,500,000
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 | Additional Paid-in Capital
Line of Credit Facility [Line Items]
Unamortized discount					$ 800,000
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 | d									30
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 | d									5
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 | d									30
Redemption price percentage									100.00%
Conversion of convertible securities				89.4314
Convertible conversion price (in dollars per share) | $ / shares				$ 11.18
Fair value disclosure				$ 97,800,000
Beneficial conversion feature				27,200,000
Unamortized discount				2,900,000
Convertible notes						110,700,000			$ 110,700,000			$ 125,000,000
Periodic principal payment									$ 0
Holding threshold required to declare debt due									25.00%
Debt issuance costs						$ 1,500,000			$ 1,500,000
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 | d									30
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 | 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
Secured Debt | Facility Agreement
Line of Credit Facility [Line Items]
Debt instrument face amount		120,000,000.0
Stated interest rate						6.87%			6.87%
Deferred finance costs, noncurrent, net		$ 5,100,000				$ 4,100,000			$ 4,100,000
Yield enhancement fee		2.25%
Periodic amortization payment		$ 40,000,000
Amount outstanding						$ 107,800,000			107,800,000
Secured Debt | Facility Agreement | Minimum
Line of Credit Facility [Line Items]
Periodic interest payment									1,500,000
Secured Debt | Facility Agreement | Maximum
Line of Credit Facility [Line Items]
Periodic interest payment									$ 12,700,000