Fair Value Measurements - Schedule of Fair Value Measurement (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Cash Equivalents and Marketable Securities:
Available-for-sale securities	$ 1,233,348	$ 1,389,634
Level 1
Cash Equivalents and Marketable Securities:
Assets, fair value	2,664	540
Other Liabilities:
Contingent consideration obligation related to Velocius acquisition		0
Level 2
Cash Equivalents and Marketable Securities:
Assets, fair value	1,233,348	1,389,595
Other Liabilities:
Contingent consideration obligation related to Velocius acquisition		0
Level 3
Cash Equivalents and Marketable Securities:
Assets, fair value	0	0
Other Liabilities:
Contingent consideration obligation related to Velocius acquisition		(900)
Money market funds \| Level 1
Cash Equivalents and Marketable Securities:
Cash equivalents	1,250	501
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
Certificates of deposit \| Level 1
Cash Equivalents and Marketable Securities:
Available-for-sale securities		39
Certificates of deposit \| Level 2
Cash Equivalents and Marketable Securities:
Available-for-sale securities		0
Certificates of deposit \| Level 3
Cash Equivalents and Marketable Securities:
Available-for-sale securities		0
Commercial paper
Cash Equivalents and Marketable Securities:
Available-for-sale securities	2,487	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	2,487	10,485
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	239,053	303,401
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	239,053	303,401
U.S. government agency obligations \| Level 3
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0	0
Mutual funds \| Level 1
Cash Equivalents and Marketable Securities:
Available-for-sale securities	1,414
Mutual funds \| Level 2
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0
Mutual funds \| Level 3
Cash Equivalents and Marketable Securities:
Available-for-sale securities	0
Corporate bonds
Cash Equivalents and Marketable Securities:
Available-for-sale securities	991,808	1,075,709
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	991,808	1,075,709
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	1,236,012	1,390,135
Other Liabilities:
Contingent consideration obligation related to Velocius acquisition		(900)
Total Fair Value \| Money market funds
Cash Equivalents and Marketable Securities:
Cash equivalents	1,250	501
Total Fair Value \| Certificates of deposit
Cash Equivalents and Marketable Securities:
Available-for-sale securities		39
Total Fair Value \| Commercial paper
Cash Equivalents and Marketable Securities:
Available-for-sale securities	2,487	10,485
Total Fair Value \| U.S. government agency obligations
Cash Equivalents and Marketable Securities:
Available-for-sale securities	239,053	303,401
Total Fair Value \| Mutual funds
Cash Equivalents and Marketable Securities:
Available-for-sale securities	1,414
Total Fair Value \| Corporate bonds
Cash Equivalents and Marketable Securities:
Available-for-sale securities	$ 991,808	$ 1,075,709

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

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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=51813488&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=49167202&loc=d3e26610-111562

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+ 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

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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

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