Description of Business	3 Months Ended
Description of Business	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business Alpine Immune Sciences, Inc. (the “Company”, “Alpine”, “we”, “us”, or “our”), together with its consolidated subsidiaries, is a clinical-stage immunotherapy company committed to leading a new wave of immune therapeutics, creating potentially powerful multifunctional immunotherapies to improve patients’ lives via unique protein engineering technologies. We have two lead programs, ALPN-101 for autoimmune/inflammatory diseases, and ALPN-202 for the treatment of cancer. Our proprietary scientific platform uses a process known as directed evolution to convert native immune system proteins into multi-targeted therapeutics potentially capable of modulating the human immune system. We were incorporated under the laws of the State of Delaware and are headquartered in Seattle, Washington. A novel strain of coronavirus, SARS-CoV-2 (“COVID-19”), was first reported in December 2019, and subsequently declared a global pandemic by the World Health Organization in March 2020. As a result of the COVID-19 outbreak, many companies have experienced disruptions in their operations and in markets served. We have implemented some and may take additional temporary precautionary measures intended to help ensure the well-being of our employees and minimize business disruption. We considered the impact of COVID-19 on the assumptions and estimates used and determined that there were no material adverse impacts to our results of operations and financial position at March 31, 2020. The full extent of the future impacts of the COVID-19 outbreak on our operations is uncertain. A prolonged outbreak may adversely impact our business, including our clinical trials. Liquidity In accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2014-15, Presentation of Financial Statements - Going Concern (“Subtopic 205-40”), our management evaluates whether there are conditions or events, considered in aggregate, that raise substantial doubt about our ability to continue as a going concern within one year after the date that the financial statements are issued. We considered such conditions or events and we expect our existing cash and cash equivalents will be sufficient to fund our operations for at least the next 12 months. In performing the assessment under Accounting Standards Codification (“ASC”) Topic 205-40, we considered that our long-term operations anticipate continuing net losses and the need for potential equity or debt financing. We also considered that new collaborations or selectively partnering our technology or programs may provide other sources of capital. However, there can be no assurances that additional funding or other sources of capital will be available on terms acceptable to us, or at all. Therefore, we developed a plan to implement cost cutting measures to reduce our working capital requirements assuming no additional planned financing. The plan includes a delay in hiring and additional reductions in personnel-related costs and other discretionary expenditures that are within our control and do not effect the anticipated timing of our clinical trials. Based off of our operating plan, it is probable that the cost cutting measures described above can be effectively implemented to allow us to meet our obligations as they become due within one year after the date that the financial statements are issued.