| Cover Cover | Aug. 16, 2019 |
| Cover page. | |
| Document Type | 8-K |
| Document Period End Date | Aug. 16, 2019 |
| Entity Registrant Name | CRAY INC. |
| Entity Incorporation, State or Country Code | WA |
| Entity File Number | 0-26820 |
| Entity Tax Identification Number | 93-0962605 |
| Entity Address, Address Line One | 901 Fifth Avenue, Suite 1000 |
| Entity Address, City or Town | Seattle, |
| Entity Address, State or Province | WA |
| Entity Address, Postal Zip Code | 98164 |
| City Area Code | 206 |
| Local Phone Number | 701-2000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.01 par value |
| Trading Symbol | CRAY |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000949158 |
| Amendment Flag | false |
