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Significant Accounting Policies - Additional Information (Detail) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2019 USD ($) Segment Customer | Mar. 31, 2018 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2012 USD ($)
Significant Accounting Policies [Line Items] |  |  |  |
Trade receivables, credit period | 30 days |  |  |
Number of operating segments | Segment | 1 |  |  |
Minimum |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Trade receivables, credit period | 30 days |  |  |
Maximum |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Trade receivables, credit period | 60 days |  |  |
Embedded Derivative Financial Instruments | BioPharma Debt |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Maximum repayment of future revenue and receivables |  |  |  | $ 150,000,000
Fair value of embedded derivative liability | $ 0 |  | $ 0 |
Gain (loss) on change in fair value of derivative liabilities | $ 0 | $ 0 |  |
Embedded Derivative Financial Instruments | BioPharma Debt | Minimum |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Derivative liability fair value assumption, coupon rate | 5.40% |  | 5.40% |
Derivative liability fair value assumptions, market yields | 8.10% |  | 6.70% |
Embedded Derivative Financial Instruments | BioPharma Debt | Maximum |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Derivative liability fair value assumption, coupon rate | 11.60% |  | 10.80% |
Derivative liability fair value assumptions, market yields | 14.90% |  | 15.80% |
Embedded Derivative Financial Instruments | BioPharma Debt | Measurement Input, Expected Term | Minimum |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Derivative liability fair value assumptions, term | 1 year 3 months 18 days |  | 1 year 3 months 18 days |
Embedded Derivative Financial Instruments | BioPharma Debt | Measurement Input, Expected Term | Maximum |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Derivative liability fair value assumptions, term | 7 years 7 months 6 days |  | 4 years |
Long-term debt from royalty-bearing instrument |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Long-term debt, discount | $ 0 |  | $ 0 |
Gross Product Sales | Customer Concentration Risk |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Number of customers | Customer | 3 |  |  |
Customer A | Gross Product Sales | Customer Concentration Risk |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Concentration risk percentage | 21.00% | 26.00% |  |
Customer A | Accounts Receivable | Customer Concentration Risk |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Concentration risk percentage | 32.00% | 37.00% |  |
Customer B | Gross Product Sales | Customer Concentration Risk |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Concentration risk percentage | 39.00% | 31.00% |  |
Customer B | Accounts Receivable | Customer Concentration Risk |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Concentration risk percentage | 37.00% | 30.00% |  |
Customer C | Gross Product Sales | Customer Concentration Risk |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Concentration risk percentage | 29.00% | 31.00% |  |
Customer C | Accounts Receivable | Customer Concentration Risk |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Concentration risk percentage | 21.00% | 24.00% |  |

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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13531-108611 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13537-108611 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592 + Details
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- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. + References No definition available. + Details
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