Borrowings - Additional Information (Detail)					3 Months Ended		12 Months Ended
	Nov. 06, 2017 USD ($) $ / shares shares	Oct. 23, 2017 USD ($) d $ / shares shares	Jun. 29, 2017 USD ($) $ / shares shares	Apr. 18, 2017 USD ($) $ / shares shares	Sep. 30, 2018 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Jul. 01, 2013 USD ($)
Debt Instrument [Line Items]
Principal amount							$ 157,800,000
Cash repayment of senior notes under exchange agreement									$ 64,287,000
Loss on extinguishment of debt							1,611,000	$ (72,024,000)	1,049,000
Cash and cash equivalents							43,946,000	22,895,000
Facility Agreement, total principle payment in 2018							24,400,000
Facility Agreement, total principle payment in 2019							30,000,000
Interest expense on notes							9,494,000	15,576,000	21,231,000
Carrying value of the milestone rights liability							12,449,000	7,937,000
Other liabilities							$ 93,500,000	$ 123,200,000
Common stock, shares issued | shares							119,053,414	95,680,831
Accretion expense - debt discount							$ 1,700,000	$ 1,722,000	$ 1,553,000
Common Stock
Debt Instrument [Line Items]
Number of shares sold in underwritten public offering | shares		973,236					173,000		1,788,000
Milestone Rights Liability
Debt Instrument [Line Items]
Other liabilities							$ 19,100,000	$ 18,400,000
Deerfield
Debt Instrument [Line Items]
Principal repayment schedule, start date							Jul. 01, 2016
Principal repayment schedule, end date							Dec. 09, 2019
Deerfield | Less portion of commitment asset
Debt Instrument [Line Items]
Senior notes, effective interest rate								8.75%
Deerfield | Milestone Rights Liability
Debt Instrument [Line Items]
Long term liability							$ 8,900,000
Deerfield | Milestone Rights Liability | Maximum
Debt Instrument [Line Items]
Contingent liability for milestone payments							90,000,000			$ 90,000,000
Senior convertible notes due December 31, 2019
Debt Instrument [Line Items]
Exchange price per share | $ / shares			$ 1.45	$ 1.22
Loss on extinguishment of debt			$ 5,000,000
Cash repayment				$ 4,000,000
Debt extinguishment amount			500,000
Debt discount and issuance costs			300,000
Senior convertible notes due December 31, 2019 | Less portion of commitment asset
Debt Instrument [Line Items]
Principal amount							54,407,000	$ 75,000,000
Loss on extinguishment of debt				300,000
Senior convertible notes due December 31, 2019 | Deerfield
Debt Instrument [Line Items]
Principal amount							$ 39,400,000	55,000,000
Senior notes, effective interest rate							9.75%
Carrying value of the milestone rights liability							$ 1,600,000
Other liabilities							8,900,000	8,900,000
Senior convertible notes due December 31, 2019 | Deerfield | Facility Agreement Third Amendment [Member]
Debt Instrument [Line Items]
Cash repayment of senior notes under exchange agreement			10,000,000
Conversion of notes to common shares, value			$ 5,000,000
Conversion Option, shares | shares			3,584,230
Exchange price per share | $ / shares			$ 1.395
Cash and cash equivalents			$ 10,000,000
Senior convertible notes due December 31, 2019 | Deerfield | Minimum | Facility Agreement Third Amendment [Member]
Debt Instrument [Line Items]
Cash and cash equivalents			$ 25,000,000				10,000,000
Senior convertible notes due December 31, 2019 | Deerfield | Less portion of commitment asset
Debt Instrument [Line Items]
Principal amount							$ 15,000,000	20,000,000
Senior notes, effective interest rate							8.75%
Cash repayment of senior notes under exchange agreement				4,000,000
Conversion of notes to common shares, value				$ 1,000,000
Senior convertible notes due December 31, 2019 | Deerfield | Tranche B Exchange Shares
Debt Instrument [Line Items]
Conversion Option, shares | shares				869,565
Exchange price per share | $ / shares				$ 1.15
Senior convertible notes due December 31, 2019 | Deerfield | Tranche B Exchange Shares | Fourth Amendment to Facility Agreement
Debt Instrument [Line Items]
Conversion of notes to common shares, value	$ 5,592,750
Conversion Option, shares | shares	1,720,846
Conversion price of shares | $ / shares	$ 3.25
Senior convertible notes due December 31, 2019 | Deerfield | Tranche 1 Notes
Debt Instrument [Line Items]
Conversion of notes to common shares, value				$ 5,000,000
Conversion Option, shares | shares				4,347,826
Senior convertible notes due December 31, 2019 | Deerfield | Milestone Rights Liability
Debt Instrument [Line Items]
Short term liability										3,200,000
Long term liability							$ 7,200,000	8,900,000		$ 13,100,000
Interest expense on notes						$ 5,800,000
Required payment pursuant to the terms of the Milestone Agreement						$ 10,000,000
Senior convertible notes due December 31, 2019 | Deerfield | Milestone Rights Liability | Scenario Forecast
Debt Instrument [Line Items]
Required payment pursuant to the terms of the Milestone Agreement					$ 5,000,000
2019 Notes and Tranche B Notes
Debt Instrument [Line Items]
Other liabilities							54,600,000	74,500,000
2019 Notes and Tranche B Notes | Fourth Amendment to Facility Agreement
Debt Instrument [Line Items]
Deferred payment of credit facility principal amount		$ 10,000,000
2019 Notes and Tranche B Notes | Deerfield | Tranche B Exchange Shares | Fourth Amendment to Facility Agreement
Debt Instrument [Line Items]
Number of trading days | d		3
Conversion price of shares | $ / shares		$ 3.25
2019 Notes and Tranche B Notes | Deerfield | Tranche B Exchange Shares | Maximum | Common Stock | Fourth Amendment to Facility Agreement
Debt Instrument [Line Items]
Number of shares sold in underwritten public offering | shares		4,000,000
5.75% Senior convertible notes due August 15, 2018
Debt Instrument [Line Items]
Principal amount		$ 27,690,000
Senior notes, effective interest rate		5.75%
Loss on extinguishment of debt							800,000
Debt discount and issuance costs							200,000	300,000
Conversion price of shares | $ / shares		$ 34
Other liabilities								22,900,000
Unamortized debt issuance costs							300,000
Unamortized premium							200,000
Accretion expense - debt discount							200,000	200,000
5.75% Senior convertible notes due October 23, 2021
Debt Instrument [Line Items]
Principal amount		$ 23,690,000					23,690,000	27,690,000
Senior notes, effective interest rate		5.75%
Number of trading days | d		10
Conversion price of shares | $ / shares		$ 5.15
Other liabilities							19,800,000
Unamortized debt issuance costs								481,000
Unamortized premium		$ 800,000					721,000	$ 426,000
No of convertible shares		194.1748
Principal amount per share | $ / shares		$ 1,000
Percentage of repurchase price		100.00%
Percentage of conversion price equaling stock price		120.00%
Consecutive trading days | d		20
Debt instrument, convertible, threshold business days		5 years
Accretion expense - debt discount							$ 30,000
5.75% Senior convertible notes due October 23, 2021 | Maximum
Debt Instrument [Line Items]
Common stock, shares issued | shares		13,648,300