Fair Value Measurements - Schedule of Fair Value Measurement (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Cash Equivalents and Marketable Securities:
Available-for-sale securities	$ 1,389,634us-gaap_AvailableForSaleSecurities	$ 913,031us-gaap_AvailableForSaleSecurities
Level 1
Cash Equivalents and Marketable Securities:
Assets, fair value	540	43,900
Other Assets:
Note receivable		0
Other Liabilities:
Contingent consideration obligation related to Velocius acquisition	0	0
Level 2
Cash Equivalents and Marketable Securities:
Assets, fair value	1,389,595	942,808
Other Assets:
Note receivable		0
Other Liabilities:
Contingent consideration obligation related to Velocius acquisition	0	0
Level 3
Cash Equivalents and Marketable Securities:
Assets, fair value	0	0
Other Assets:
Note receivable		22,879
Other Liabilities:
Contingent consideration obligation related to Velocius acquisition	(900)	(2,600)
Money market funds \| Level 1
Cash Equivalents and Marketable Securities:
Cash equivalents	501	40,482
Money market funds \| Level 2
Cash Equivalents and Marketable Securities:
Cash equivalents	0	0
Money market funds \| Level 3
Cash Equivalents and Marketable Securities:
Cash equivalents	0	0
Certificates of deposit
Cash Equivalents and Marketable Securities:
Available-for-sale securities	39	222
Certificates of deposit \| Level 1
Cash Equivalents and Marketable Securities:
Available-for-sale securities	39	3,418
Certificates of deposit \| Level 2
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0	0
Certificates of deposit \| Level 3
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0	0
Commercial paper
Cash Equivalents and Marketable Securities:
Available-for-sale securities	10,485
Commercial paper \| Level 1
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0	0
Commercial paper \| Level 2
Cash Equivalents and Marketable Securities:
Available-for-sale securities	10,485	29,999
Commercial paper \| Level 3
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0	0
U.S. government agency obligations
Cash Equivalents and Marketable Securities:
Available-for-sale securities	303,401	174,948
U.S. government agency obligations \| Level 1
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0	0
U.S. government agency obligations \| Level 2
Cash Equivalents and Marketable Securities:
Available-for-sale securities	303,401	174,948
U.S. government agency obligations \| Level 3
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0	0
Corporate bonds
Cash Equivalents and Marketable Securities:
Available-for-sale securities	1,075,709	737,861
Corporate bonds \| Level 1
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0	0
Corporate bonds \| Level 2
Cash Equivalents and Marketable Securities:
Available-for-sale securities	1,075,709	737,861
Corporate bonds \| Level 3
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0	0
Total Fair Value
Cash Equivalents and Marketable Securities:
Assets, fair value	1,390,135	986,708
Other Assets:
Note receivable		22,879
Other Liabilities:
Contingent consideration obligation related to Velocius acquisition	(900)	(2,600)
Total Fair Value \| Money market funds
Cash Equivalents and Marketable Securities:
Cash equivalents	501	40,482
Total Fair Value \| Certificates of deposit
Cash Equivalents and Marketable Securities:
Available-for-sale securities	39	3,418
Total Fair Value \| Commercial paper
Cash Equivalents and Marketable Securities:
Available-for-sale securities	10,485	29,999
Total Fair Value \| U.S. government agency obligations
Cash Equivalents and Marketable Securities:
Available-for-sale securities	303,401	174,948
Total Fair Value \| Corporate bonds
Cash Equivalents and Marketable Securities:
Available-for-sale securities	$ 1,075,709	$ 737,861

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

+ Details

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of obligations measured on a recurring basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a),(b)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisObligations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LiabilitiesFairValueDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value portion of an agreement for an unconditional promise by the maker to pay the holder a definite sum of money at a future date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Subparagraph b

-Article 5

+ Details

Name:	us-gaap_NotesReceivableFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_OtherLiabilitiesDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_DomesticCorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: