Annual report pursuant to Section 13 and 15(d)

Composition of Certain Financial Statement Captions - Summary of available-for-sale securities' adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category (Details)

v2.4.1.9
Composition of Certain Financial Statement Captions - Summary of available-for-sale securities' adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis $ 386,791us-gaap_AvailableForSaleSecuritiesAmortizedCost $ 361,183us-gaap_AvailableForSaleSecuritiesAmortizedCost
Unrealized Gains 6p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax 6p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
Unrealized Losses (453)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax (262)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
Available-for-sale Securities 386,344us-gaap_AvailableForSaleSecurities 360,927us-gaap_AvailableForSaleSecurities
Money market funds    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 89,113us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember 		98,437us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
Unrealized Gains 0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember 		0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
Unrealized Losses 0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember 		0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
Available-for-sale Securities 89,113us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember 		98,437us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
Commercial paper    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 54,792us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember 		101,773us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember
Unrealized Gains 0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember 		0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember
Unrealized Losses 0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember 		0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember
Available-for-sale Securities 54,792us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember 		101,773us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember
Corporate debt securities    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 235,135us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember 		155,273us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
Unrealized Gains 6p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember 		6p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
Unrealized Losses (444)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember 		(258)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
Available-for-sale Securities 234,697us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember 		155,021us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
U.S. government and government agency debt securities    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 7,751us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		5,700us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Unrealized Gains 0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Unrealized Losses (9)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		(4)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Available-for-sale Securities $ 7,742us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		$ 5,696us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember