| Document and Entity Information | Nov. 03, 2019 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001561660 |
| Document Type | 8-K |
| Document Period End Date | Nov. 3, 2019 |
| Entity Registrant Name | PATTERN ENERGY GROUP INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-36087 |
| Entity Tax Identification Number | 90-0893251 |
| Entity Address, Address Line One | 1088 Sansome Street |
| Entity Address, City or Town | San Francisco |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94111 |
| City Area Code | (415) |
| Local Phone Number | 283-4000 |
| Written Communications | false |
| Soliciting Material | true |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Class A [Member] | |
| Document And Entity Information [Line Items] | |
| Security Exchange Name | NASDAQ |
| Security 12b Title | Class A common stock |
| Trading Symbol | PEGI |
| M 0 [Member] | |
| Document And Entity Information [Line Items] | |
| Security Exchange Name | CHX |
