Borrowings - Facility Financing Obligation (2019 Notes and Tranche B Notes) - Additional Information (Detail)													1 Months Ended		3 Months Ended	12 Months Ended
	Sep. 26, 2018 USD ($)	Sep. 05, 2018 USD ($) shares	Jul. 12, 2018 USD ($) $ / shares shares	Jun. 08, 2018 USD ($) $ / shares shares	Mar. 12, 2018 USD ($) shares	Mar. 06, 2018 USD ($) d $ / shares shares	Jan. 18, 2018 USD ($) d $ / shares shares	Jan. 15, 2018 USD ($)	Nov. 06, 2017 USD ($) $ / 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 ($)	Aug. 31, 2018 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Oct. 31, 2018 USD ($)	Oct. 16, 2018 USD ($)	Sep. 07, 2018 $ / shares	Sep. 06, 2018 $ / shares	Jun. 07, 2018 USD ($) $ / shares	Mar. 09, 2018 $ / shares
Debt Instrument [Line Items]
Principal amount																$ 101,700,000
Loss on extinguishment of debt																765,000	$ 1,611,000	$ (72,024,000)
Cash and cash equivalents																$ 71,157,000	$ 43,946,000
Common stock, shares issued | shares																187,029,967	119,053,414
Milestone rights liability																$ 7,201,000	$ 7,201,000
Common Stock
Debt Instrument [Line Items]
Number of shares sold in underwritten public offering | shares										973,236
Deerfield
Debt Instrument [Line Items]
Conversion Option, shares | shares				3,061,224
Exchange price per share | $ / shares			$ 1.80	$ 1.96								$ 1.15									$ 1.78	$ 2.04
Loss on extinguishment of debt			$ 0													$ 700,000
Cash and cash equivalents				$ 20,000,000
Debt discount and issuance costs		$ 300,000
Common stock, shares issued | shares			7,367,839
Debt instrument, payment terms description																further defer the payment of $3.0 million in principal amount of 2019 notes from September 30, 2018 until the earlier of October 31, 2018 or the first business day following the date the Company receives an upfront payment of $45.0 million from UT
Available amount of credit facility under covenant restrictions for each quarter end after current fiscal	$ 25,000,000															$ 25,000,000
Deerfield | United Therapeutics Corporation
Debt Instrument [Line Items]
Upfront payment received																				$ 45,000,000
Deerfield | Minimum
Debt Instrument [Line Items]
Cash and cash equivalents																							$ 25,000,000
Available amount of credit facility under covenant restrictions																20,000,000			$ 20,000,000
Deerfield | Minimum | Common Stock
Debt Instrument [Line Items]
Conversion price of shares | $ / shares			$ 1.80
Deerfield | Maximum | Common Stock
Debt Instrument [Line Items]
Conversion Option, shares | shares			5,750,000
Conversion price of shares | $ / shares			$ 2.01
2019 notes
Debt Instrument [Line Items]
Principal amount																$ 9,000,000	39,400,000
Senior notes, effective interest rate																9.75%
Conversion of notes to common shares, value						$ 1,300,000
Exchange price per share | $ / shares						$ 2.83					$ 1.45
Loss on extinguishment of debt											$ 5,000,000
Debt extinguishment amount											500,000
Debt discount and issuance costs											300,000
Number of trading days | d						3
2019 notes | Common Stock
Debt Instrument [Line Items]
Conversion Option, shares | shares						441,618
2019 notes | Deerfield
Debt Instrument [Line Items]
Senior notes, effective interest rate																9.75%
Cash repayment of senior notes under exchange agreement	$ 3,000,000										10,000,000		$ 3,000,000	$ 3,000,000
Conversion of notes to common shares, value		8,000,000									$ 5,000,000	$ 5,000,000
Conversion Option, shares | shares											3,584,230	4,347,826
Exchange price per share | $ / shares											$ 1.395
Cash and cash equivalents											$ 10,000,000
2019 notes | Deerfield | 2019 Notes Due And Payable On July 1, 2018
Debt Instrument [Line Items]
Principal amount				5,000,000
Conversion of notes to common shares, value				3,000,000
2019 notes | Deerfield | Notes Due and Payable on July 18, 2018
Debt Instrument [Line Items]
Principal amount			$ 10,000,000
Conversion of notes to common shares, value			7,000,000
2019 notes | Deerfield | Notes Due And Payable On December312019
Debt Instrument [Line Items]
Principal amount			5,000,000
Conversion of notes to common shares, value			3,000,000
2019 notes | Deerfield | Minimum
Debt Instrument [Line Items]
Cash and cash equivalents											$ 25,000,000					$ 10,000,000
Tranche B notes
Debt Instrument [Line Items]
Principal amount																$ 2,500,000	15,000,000
Senior notes, effective interest rate																8.75%
Tranche B notes | Deerfield
Debt Instrument [Line Items]
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		$ 2,500,000			$ 5,000,000							$ 1,000,000
Conversion Option, shares | shares					1,838,236							869,565
Exchange price per share | $ / shares																								$ 2.72
Tranche B notes | Deerfield | Tranche B Notes Due and Payable on December 31, 2019
Debt Instrument [Line Items]
Principal amount				5,000,000
Conversion of notes to common shares, value				$ 3,000,000
Tranche B notes | Deerfield | Notes Due And Payable On December312019
Debt Instrument [Line Items]
Principal amount			2,000,000
Conversion of notes to common shares, value			$ 2,000,000
Facility Financing Obligation
Debt Instrument [Line Items]
Principal amount																$ 11,495,000	54,407,000
Principal repayment schedule, start date																Jul. 01, 2016
Principal repayment schedule, end date																Jul. 31, 2019
Facility agreement, total principle payment in 2019																$ 11,500,000
Exchange price per share | $ / shares												$ 1.22
Loss on extinguishment of debt												$ 300,000
Cash repayment												$ 4,000,000
Deferred payment of credit facility principal amount										$ 10,000,000
Facility Financing Obligation | Deerfield
Debt Instrument [Line Items]
Conversion of notes to common shares, value							$ 3,200,000		$ 5,592,750
Conversion Option, shares | shares									1,720,846
Exchange price per share | $ / shares							$ 2.49
Deferred payment of credit facility principal amount							$ 1,300,000	$ 4,400,000
Number of trading days | d							3			3
Conversion price of shares | $ / shares				$ 2.01			$ 2.75		$ 3.25	$ 3.25													$ 2.75
Common stock, shares issued | shares							1,267,972
Milestone rights liability																7,200,000	7,200,000
Remaining milestone rights liability																8,900,000	$ 8,900,000
Facility Financing Obligation | Deerfield | Scenario Forecast
Debt Instrument [Line Items]
Required payment for milestone liability															$ 5,000,000
Facility Financing Obligation | Deerfield | Accrued Expenses and Other Current Liabilities
Debt Instrument [Line Items]
Milestone rights liability, current																$ 1,600,000
Facility Financing Obligation | Deerfield | Common Stock
Debt Instrument [Line Items]
Conversion Option, shares | shares		5,749,500
Number of shares sold in underwritten public offering | shares							10,000,000
Facility Financing Obligation | Deerfield | Maximum
Debt Instrument [Line Items]
Conversion Option, shares | shares				9,558,382
Facility Financing Obligation | Deerfield | Maximum | Common Stock
Debt Instrument [Line Items]
Number of shares sold in underwritten public offering | shares										4,000,000