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Stockholders' Equity - Additional Information (Detail) (Sixth Share Repurchase Program, USD $) In Millions, unless otherwise specified | Sep. 30, 2014 | Nov. 30, 2013
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Sixth Share Repurchase Program |  |
Stockholders Equity Note [Line Items] |  |
Share repurchase program, authorized amount |  | $ 300
Share repurchase program, remaining authorized repurchase amount | $ 120 |

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- Details
Name: | mygn_StockholdersEquityNoteLineItems
Namespace Prefix: | mygn_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of stock repurchase plan authorized. + References No definition available. + Details
Name: | us-gaap_StockRepurchaseProgramAuthorizedAmount1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount remaining of a stock repurchase plan authorized. + References No definition available. + Details
Name: | us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant