| Cover | 12 Months Ended |
| Dec. 31, 2022 | |
| Document Information [Line Items] | |
| Document Type | DEF 14A |
| Amendment Flag | false |
| Entity Information [Line Items] | |
| Entity Registrant Name | Alnylam Pharmaceuticals, Inc. |
| Entity Central Index Key | 0001178670 |
| Pay vs Performance Disclosure - USD ($) | 12 Months Ended | ||
| Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | |
| Pay vs Performance Disclosure [Table] | |||
| Pay vs Performance [Table Text Block] | Pay Versus Performance Table Value of Initial Fixed $100 (in thousands) Year Summary Compensation Average Summary non-PEO Average non-PEO NEOs TSR ($) (6) Peer Group Net Loss ($) Company (CSM) - Net 2022 4,588,810 30,375,480 3,580,510 17,466,190 206.35 113.65 (1,131,156 ) 894,329 2021 10,176,685 17,514,345 5,918,910 10,714,290 147.24 126.45 (852,824 ) 662,138 2020 7,818,164 17,306,949 4,240,550 6,617,560 112.85 126.42 (858,281 ) 361,520 (1) For 2022, our PEO was Yvonne L. Greenstreet, MBChB, MBA. For 2021 and 2020, our PEO was John M. Maraganore, Ph.D. (2) For 2022, our non-PEO Akshay K. Vaishnaw, Jeffrey V. Poulton, Pushkal P. Garg, M.D., and Indrani L. Franchini, J.D. non-PEO non-PEO (3) Following is a summary of the adjustments made to PEO compensation as reported in the Summary Compensation Table to determine PEO CAP as reported in this table: 2022 2021 2020 Total Compensation Reported in SCT 4,588,810 10,176,685 7,818,164 LESS: the grant date fair value of equity awards granted in the year indicated (2,498,790 ) (7,861,410 ) (5,746,295 ) ADD: the year-end 18,073,160 9,100,080 14,001,000 ADD: the change in fair value of equity awards granted years prior to the year indicated that were outstanding and unvested at the end of the year indicated (as compared to fair value at the end of the immediately prior year) (a) 6,436,300 2,419,780 953,260 ADD: the change in fair value of equity awards granted years prior to the year indicated that vested in the year indicated (fair value at vesting date as compared to the end of the immediately prior year) (a) 3,776,000 3,679,210 280,820 Total (Net) Adjustments 30,375,480 17,514,345 17,306,949 (a) We determined the year-end (4) Following is a summary of the adjustments made to average non-PEO non-PEO 2022 2021 2020 Average Total Compensation Reported in SCT 3,580,510 5,918,910 4,240,550 LESS: the grant date fair value of equity awards granted in the year indicated (2,548,800 ) (4,891,560 ) (3,113,250 ) ADD: the year-end 11,045,880 6,583,990 4,670,300 ADD: the change in fair value of equity awards granted years prior to the year indicated that were outstanding and unvested at the end of the year indicated (as compared to fair value at the end of the immediately prior year) (a) 3,343,110 962,260 450,100 ADD: the change in fair value of equity awards granted years prior to the year indicated that vested in the year indicated (fair value at vesting date as compared to the end of the immediately prior year) (a) 2,045,490 2,140,690 369,860 Total (Net) Adjustments 17,466,190 10,714,290 6,617,560 (a) We determined the year-end (5) In calculating CAP reflected in these columns, the fair value or change in fair value, as applicable, of the equity award adjustments included in such calculations were computed in accordance with FASB ASC Topic 718. We did not report a change in pension benefit values for any of the years reflected in the table, and therefore adjustments to pension benefit values were not included in calculating CAP reflected in these columns, because we do not sponsor, maintain or contribute to a defined benefit pension plan. (6) The Company TSR and the Company’s Peer Group TSR reflected in these columns for each applicable fiscal year is calculated based on a fixed investment of $100 at the applicable measurement point on the same cumulative basis as is used in Item 201(e) of Regulation S-K. 10-K S-K: Total Return X | ||
| Company Selected Measure Name | NetProductRevenue | ||
| Named Executive Officers, Footnote [Text Block] | Akshay K. Vaishnaw, Jeffrey V. Poulton, Pushkal P. Garg, M.D., and Indrani L. Franchini, J.D. | Dr. Greenstreet, Dr. Vaishnaw, Mr. Poulton, and Mr. Tanguler. | Dr. Greenstreet, Dr. Vaishnaw, Mr. Poulton, Laurie B. Keating, and Barry E. Greene. |
| Peer Group Issuers, Footnote [Text Block] | The Company TSR and the Company’s Peer Group TSR reflected in these columns for each applicable fiscal year is calculated based on a fixed investment of $100 at the applicable measurement point on the same cumulative basis as is used in Item 201(e) of Regulation S-K. 10-K S-K: Total Return X | ||
| PEO Total Compensation Amount | $ 4,588,810 | $ 10,176,685 | $ 7,818,164 |
| PEO Actually Paid Compensation Amount | $ 30,375,480 | 17,514,345 | 17,306,949 |
| Adjustment To PEO Compensation, Footnote [Text Block] | (3) Following is a summary of the adjustments made to PEO compensation as reported in the Summary Compensation Table to determine PEO CAP as reported in this table: 2022 2021 2020 Total Compensation Reported in SCT 4,588,810 10,176,685 7,818,164 LESS: the grant date fair value of equity awards granted in the year indicated (2,498,790 ) (7,861,410 ) (5,746,295 ) ADD: the year-end 18,073,160 9,100,080 14,001,000 ADD: the change in fair value of equity awards granted years prior to the year indicated that were outstanding and unvested at the end of the year indicated (as compared to fair value at the end of the immediately prior year) (a) 6,436,300 2,419,780 953,260 ADD: the change in fair value of equity awards granted years prior to the year indicated that vested in the year indicated (fair value at vesting date as compared to the end of the immediately prior year) (a) 3,776,000 3,679,210 280,820 Total (Net) Adjustments 30,375,480 17,514,345 17,306,949 (a) We determined the year-end | ||
| Non-PEO NEO Average Total Compensation Amount | $ 3,580,510 | 5,918,910 | 4,240,550 |
| Non-PEO NEO Average Compensation Actually Paid Amount | $ 17,466,190 | 10,714,290 | 6,617,560 |
| Adjustment to Non-PEO NEO Compensation Footnote [Text Block] | (4) Following is a summary of the adjustments made to average non-PEO non-PEO 2022 2021 2020 Average Total Compensation Reported in SCT 3,580,510 5,918,910 4,240,550 LESS: the grant date fair value of equity awards granted in the year indicated (2,548,800 ) (4,891,560 ) (3,113,250 ) ADD: the year-end 11,045,880 6,583,990 4,670,300 ADD: the change in fair value of equity awards granted years prior to the year indicated that were outstanding and unvested at the end of the year indicated (as compared to fair value at the end of the immediately prior year) (a) 3,343,110 962,260 450,100 ADD: the change in fair value of equity awards granted years prior to the year indicated that vested in the year indicated (fair value at vesting date as compared to the end of the immediately prior year) (a) 2,045,490 2,140,690 369,860 Total (Net) Adjustments 17,466,190 10,714,290 6,617,560 (a) We determined the year-end | ||
| Compensation Actually Paid vs. Total Shareholder Return [Text Block] | |||
| Compensation Actually Paid vs. Net Income [Text Block] | |||
| Compensation Actually Paid vs. Company Selected Measure [Text Block] | |||
| Total Shareholder Return Vs Peer Group [Text Block] | |||
| Total Shareholder Return Amount | $ 206.35 | 147.24 | 112.85 |
| Peer Group Total Shareholder Return Amount | 113.65 | 126.45 | 126.42 |
| Net Income (Loss) | $ (1,131,156,000) | $ (852,824,000) | $ (858,281,000) |
| Company Selected Measure Amount | 894,329,000 | 662,138,000 | 361,520,000 |
| PEO Name | Yvonne L. Greenstreet | John M. Maraganore | John M. Maraganore |
| PEO [Member] | the grant date fair value of equity awards granted in the year indicated [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | $ (2,498,790) | $ (7,861,410) | $ (5,746,295) |
| PEO [Member] | the yearend fair value of outstanding and unvested equity awards granted in the year indicated (a) [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 18,073,160 | 9,100,080 | 14,001,000 |
| PEO [Member] | the change in fair value of equity awards granted years prior to the year indicated that were outstanding and unvested at the end of the year indicated (as compared to fair value at the end of the immediately prior year) (a) [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 6,436,300 | 2,419,780 | 953,260 |
| PEO [Member] | the change in fair value of equity awards granted years prior to the year indicated that vested in the year indicated (fair value at vesting date as compared to the end of the immediately prior year) (a) [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 3,776,000 | 3,679,210 | 280,820 |
| Non-PEO NEO [Member] | the grant date fair value of equity awards granted in the year indicated [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (2,548,800) | (4,891,560) | (3,113,250) |
| Non-PEO NEO [Member] | the yearend fair value of outstanding and unvested equity awards granted in the year indicated (a) [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 11,045,880 | 6,583,990 | 4,670,300 |
| Non-PEO NEO [Member] | the change in fair value of equity awards granted years prior to the year indicated that were outstanding and unvested at the end of the year indicated (as compared to fair value at the end of the immediately prior year) (a) [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 3,343,110 | 962,260 | 450,100 |
| Non-PEO NEO [Member] | the change in fair value of equity awards granted years prior to the year indicated that vested in the year indicated (fair value at vesting date as compared to the end of the immediately prior year) (a) [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | $ 2,045,490 | $ 2,140,690 | $ 369,860 |
