Recent Accounting Pronouncements Level 1 (Notes)	9 Months Ended
Sep. 30, 2018
Recent Accounting Pronouncements [Abstract]
New Accounting Pronouncements, Policy	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, “Revenue from Contracts with Customers”, which amends FASB ASC Topic 606. ASU 2014-09 provides a single, comprehensive revenue recognition model for all contracts with customers. This standard contains principles for the determination of the measurement of revenue and the timing of when such revenue is recognized. Revenue recognition will reflect the transfer of goods or services to customers at an amount that is expected to be earned in exchange for those goods or services. In 2015, the FASB issued ASU No. 2015-14, “Revenue from Contracts with Customers: Deferral of Effective Date”, which deferred the effective date by one year to annual periods after December 15, 2017 including interim periods within that reporting period. In 2016, the FASB issued four additional ASUs related to Topic 606: ASU Nos. 2016-08, 2016-10, 2016-12 and 2016-20. These ASUs clarify various aspects of the new revenue guidance, including principal versus agent considerations, identifying performance obligations and licensing, and they include other improvements and practical expedients. The Company adopted this new standard on January 1, 2018 using the modified retrospective transition method, and has applied the provisions to contracts that were not complete as of January 1, 2018. Impact of Adoption The Company recognizes product revenue when the customer obtains control of the product, which occurs upon delivery. Product revenue is recorded net of applicable reserves for variable consideration, including discounts and allowances. These estimates are based on the most likely amount method for relevant factors such as current contractual and statutory requirements, industry data and forecasted customer buying and payment patterns. The Company’s net product revenues reflect the Company’s best estimates of the amount of consideration to which it is entitled based on the terms of the respective underlying contracts. The adoption of this ASU did not impact the timing or amount of revenues recognized related to its contracts with customers for the sale of product. The Company’s primary source of collaboration revenue has been through its license and collaboration agreements with three separate third-party licensees: Texas Institute for Genomic Medicine (“TIGM”), Sanofi and Ipsen. With respect to its contract with TIGM, the Company evaluated the variable consideration relating to the remaining milestone and determined, based on the most likely amount method, that it was not probable that a significant reversal would occur and therefore, concluded no constraint was required. Accordingly, the Company recorded a $14.2 million cumulative-effect adjustment to its accumulated deficit as of January 1, 2018 and reduced deferred revenue in the same amount. With respect to its collaboration agreements with Sanofi and Ipsen, the Company evaluated the variable consideration relating to future milestone payments and determined, based on the most likely amount method, that the estimated amounts could be considered as part of the transaction price. The Company then evaluated the variable constraint and determined that the variable consideration amounts are constrained, primarily by future events that are not within the control of the Company. The future events primarily relate to receipt of positive results from studies, approval from regulatory agencies, and upon achieving sales in certain locations. Accordingly, the Company determined that there was no cumulative adjustment required for these agreements on the date of adoption. In February 2016, the FASB issued ASU No. 2016-02, “Leases.” ASU 2016-02 requires companies that lease assets to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, in its balance sheet. The pronouncement will also require additional disclosures about the amount, timing and uncertainty of cash flows arising from leases. This pronouncement is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018, and early adoption is permitted. This ASU is required to be adopted using a modified retrospective approach. Management plans to adopt ASU 2016-02 on January 1, 2019, and expects the adoption of this ASU to result in the recognition of additional assets and corresponding liabilities on the consolidated balance sheets, primarily related to leases of office space. The Company does not expect that the implementation of the ASU will have a material impact on its financial position. The actual impact will depend on the Company’s lease portfolio at the time of adoption. The Company continues to assess all implications of the standard and related financial disclosures.

Recent Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, “Revenue from Contracts with Customers”, which amends FASB ASC Topic 606. ASU 2014-09 provides a single, comprehensive revenue recognition model for all contracts with customers. This standard contains principles for the determination of the measurement of revenue and the timing of when such revenue is recognized. Revenue recognition will reflect the transfer of goods or services to customers at an amount that is expected to be earned in exchange for those goods or services. In 2015, the FASB issued ASU No. 2015-14, “Revenue from Contracts with Customers: Deferral of Effective Date”, which deferred the effective date by one year to annual periods after December 15, 2017 including interim periods within that reporting period. In 2016, the FASB issued four additional ASUs related to Topic 606: ASU Nos. 2016-08, 2016-10, 2016-12 and 2016-20. These ASUs clarify various aspects of the new revenue guidance, including principal versus agent considerations, identifying performance obligations and licensing, and they include other improvements and practical expedients. The Company adopted this new standard on January 1, 2018 using the modified retrospective transition method, and has applied the provisions to contracts that were not complete as of January 1, 2018.

Impact of Adoption

The Company recognizes product revenue when the customer obtains control of the product, which occurs upon delivery. Product revenue is recorded net of applicable reserves for variable consideration, including discounts and allowances. These estimates are based on the most likely amount method for relevant factors such as current contractual and statutory requirements, industry data and forecasted customer buying and payment patterns. The Company’s net product revenues reflect the Company’s best estimates of the amount of consideration to which it is entitled based on the terms of the respective underlying contracts. The adoption of this ASU did not impact the timing or amount of revenues recognized related to its contracts with customers for the sale of product.

The Company’s primary source of collaboration revenue has been through its license and collaboration agreements with three separate third-party licensees: Texas Institute for Genomic Medicine (“TIGM”), Sanofi and Ipsen. With respect to its contract with TIGM, the Company evaluated the variable consideration relating to the remaining milestone and determined, based on the most likely amount method, that it was not probable that a significant reversal would occur and therefore, concluded no constraint was required. Accordingly, the Company recorded a $14.2 million cumulative-effect adjustment to its accumulated deficit as of January 1, 2018 and reduced deferred revenue in the same amount.

With respect to its collaboration agreements with Sanofi and Ipsen, the Company evaluated the variable consideration relating to future milestone payments and determined, based on the most likely amount method, that the estimated amounts could be considered as part of the transaction price. The Company then evaluated the variable constraint and determined that the variable consideration amounts are constrained, primarily by future events that are not within the control of the Company. The future events primarily relate to receipt of positive results from studies, approval from regulatory agencies, and upon achieving sales in certain locations. Accordingly, the Company determined that there was no cumulative adjustment required for these agreements on the date of adoption.

In February 2016, the FASB issued ASU No. 2016-02, “Leases.” ASU 2016-02 requires companies that lease assets to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, in its balance sheet. The pronouncement will also require additional disclosures about the amount, timing and uncertainty of cash flows arising from leases. This pronouncement is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018, and early adoption is permitted. This ASU is required to be adopted using a modified retrospective approach. Management plans to adopt ASU 2016-02 on January 1, 2019, and expects the adoption of this ASU to result in the recognition of additional assets and corresponding liabilities on the consolidated balance sheets, primarily related to leases of office space. The Company does not expect that the implementation of the ASU will have a material impact on its financial position. The actual impact will depend on the Company’s lease portfolio at the time of adoption. The Company continues to assess all implications of the standard and related financial disclosures.