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Marketable Investment Securities - Schedule of Fair Value for Available-for-Sale Securities by Major Security Type and Class of Security (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Jun. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 229,467us-gaap_AvailableForSaleSecuritiesAmortizedCost	$ 270,224us-gaap_AvailableForSaleSecuritiesAmortizedCost
Gross unrealized holding gains	148us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax	383us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Gross unrealized holding losses	(62)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax	(21)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Estimated fair value	229,553us-gaap_AvailableForSaleSecurities	270,586us-gaap_AvailableForSaleSecurities
Cash
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	57,010us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_CashMember	45,181us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_CashMember
Estimated fair value	57,010us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_CashMember	45,181us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_CashMember
Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,699us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_CashEquivalentsMember	19,639us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_CashEquivalentsMember
Gross unrealized holding gains		1us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_CashEquivalentsMember
Estimated fair value	2,699us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_CashEquivalentsMember	19,640us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_CashEquivalentsMember
Restricted Cash
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	22,138us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = mygn_RestrictedCashMember
Estimated fair value	22,138us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = mygn_RestrictedCashMember
Total Cash, Cash Equivalents and Restricted Cash
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	81,847us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = mygn_CashCashEquivalentsAndRestrictedCashMember
Estimated fair value	81,847us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = mygn_CashCashEquivalentsAndRestrictedCashMember
Corporate Bonds And Notes
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	45,181us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember	44,449us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Gross unrealized holding gains	5us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember	36us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Gross unrealized holding losses	(18)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember	(11)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Estimated fair value	45,168us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember	44,474us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	83,506us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember	137,821us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember
Gross unrealized holding gains	141us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember	334us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember
Gross unrealized holding losses	(40)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember	(3)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember
Estimated fair value	83,607us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember	138,152us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember
Federal Agency Issues
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	18,933us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_USTreasuryAndGovernmentMember	23,134us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_USTreasuryAndGovernmentMember
Gross unrealized holding gains	2us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_USTreasuryAndGovernmentMember	12us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_USTreasuryAndGovernmentMember
Gross unrealized holding losses	(4)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_USTreasuryAndGovernmentMember	(7)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_USTreasuryAndGovernmentMember
Estimated fair value	18,931us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_USTreasuryAndGovernmentMember	23,139us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_USTreasuryAndGovernmentMember
Total Cash And Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		64,820us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_CashAndCashEquivalentsMember
Gross unrealized holding gains		1us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_CashAndCashEquivalentsMember
Estimated fair value		64,821us-gaap_AvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = us-gaap_CashAndCashEquivalentsMember
Total Available For Sale
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	147,620us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember	205,404us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember
Gross unrealized holding gains	148us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember	382us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember
Gross unrealized holding losses	(62)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember	(21)us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember
Estimated fair value	$ 147,706us-gaap_AvailableForSaleSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember	$ 205,765us-gaap_AvailableForSaleSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = us-gaap_AvailableforsaleSecuritiesMember

X

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

+ References

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-Publisher FASB

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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