Quarterly report pursuant to Section 13 or 15(d)

Cash, Cash Equivalents and Investments - 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
Cash, Cash Equivalents and Investments - Summary of available-for-sale securities' adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category (Details) (USD $)
Mar. 31, 2015
Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]    
Adjusted Cost $ 387,273,000p_CashEquivalentsAndShortTermInvestmentsAmortizedCost $ 386,791,000p_CashEquivalentsAndShortTermInvestmentsAmortizedCost
Unrealized Gains 271,000p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax 6,000p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
Unrealized Losses (160,000)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax (453,000)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
Fair Value 387,384,000p_CashEquivalentsAndShortTermInvestmentsFairValueDisclosure 386,344,000p_CashEquivalentsAndShortTermInvestmentsFairValueDisclosure
Money market funds    
Schedule of Available-for-sale Securities [Line Items]    
Adjusted Cost 93,160,000p_CashEquivalentsAndShortTermInvestmentsAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember 		89,113,000p_CashEquivalentsAndShortTermInvestmentsAmortizedCost
/ 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
Fair Value 93,160,000p_CashEquivalentsAndShortTermInvestmentsFairValueDisclosure
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember 		89,113,000p_CashEquivalentsAndShortTermInvestmentsFairValueDisclosure
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
Commercial paper    
Schedule of Available-for-sale Securities [Line Items]    
Adjusted Cost 52,834,000p_CashEquivalentsAndShortTermInvestmentsAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember 		54,792,000p_CashEquivalentsAndShortTermInvestmentsAmortizedCost
/ 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
Fair Value 52,834,000p_CashEquivalentsAndShortTermInvestmentsFairValueDisclosure
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember 		54,792,000p_CashEquivalentsAndShortTermInvestmentsFairValueDisclosure
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember
Corporate debt securities    
Schedule of Available-for-sale Securities [Line Items]    
Adjusted Cost 233,528,000p_CashEquivalentsAndShortTermInvestmentsAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember 		235,135,000p_CashEquivalentsAndShortTermInvestmentsAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
Unrealized Gains 269,000p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember 		6,000p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
Unrealized Losses (154,000)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember 		(444,000)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
Fair Value 233,643,000p_CashEquivalentsAndShortTermInvestmentsFairValueDisclosure
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember 		234,697,000p_CashEquivalentsAndShortTermInvestmentsFairValueDisclosure
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
U.S. government and government agency debt securities    
Schedule of Available-for-sale Securities [Line Items]    
Adjusted Cost 7,751,000p_CashEquivalentsAndShortTermInvestmentsAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		7,751,000p_CashEquivalentsAndShortTermInvestmentsAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Unrealized Gains 2,000p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		0p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Unrealized Losses (6,000)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		(9,000)p_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Fair Value $ 7,747,000p_CashEquivalentsAndShortTermInvestmentsFairValueDisclosure
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		$ 7,742,000p_CashEquivalentsAndShortTermInvestmentsFairValueDisclosure
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember