Fair Value Measurements (Assets And Liabilities Measured At Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets
Total	$ 903,709	$ 633,110
Liabilities
Long-term debt	46,285	48,982
Contingent purchase consideration	902	902
Total	47,187	49,884
Level 1
Assets
Total	649,162	632,078
Liabilities
Long-term debt	0	0
Contingent purchase consideration	0	0
Total	0	0
Level 2
Assets
Total	253,580	16
Liabilities
Long-term debt	46,285	48,982
Contingent purchase consideration	0	0
Total	46,285	48,982
Level 3
Assets
Total	967	1,016
Liabilities
Long-term debt	0	0
Contingent purchase consideration	902	902
Total	902	902
Money market fund deposits and term deposits
Assets
Cash equivalents	316,442	425,917
Money market fund deposits and term deposits \| Level 1
Assets
Cash equivalents	316,442	425,917
Money market fund deposits and term deposits \| Level 2
Assets
Cash equivalents	0	0
Money market fund deposits and term deposits \| Level 3
Assets
Cash equivalents	0	0
U.S. Treasury and agency obligations
Assets
Cash equivalents	8,999
Short-term investments	113,094	41,217
U.S. Treasury and agency obligations \| Level 1
Assets
Cash equivalents	8,999
Short-term investments	113,094	41,217
U.S. Treasury and agency obligations \| Level 2
Assets
Cash equivalents	0
Short-term investments	0	0
U.S. Treasury and agency obligations \| Level 3
Assets
Cash equivalents	0
Short-term investments	0	0
Commercial paper
Assets
Cash equivalents	89,312
Commercial paper \| Level 1
Assets
Cash equivalents	0
Commercial paper \| Level 2
Assets
Cash equivalents	89,312
Commercial paper \| Level 3
Assets
Cash equivalents	0
Corporate bonds
Assets
Short-term investments	196,856	131,048
Long-term investments and other assets	13,771
Corporate bonds \| Level 1
Assets
Short-term investments	196,856	131,048
Long-term investments and other assets	13,771
Corporate bonds \| Level 2
Assets
Short-term investments	0	0
Long-term investments and other assets	0
Corporate bonds \| Level 3
Assets
Short-term investments	0	0
Long-term investments and other assets	0
Commercial paper, not included in cash equivalents
Assets
Short-term investments	164,255	33,896
Commercial paper, not included in cash equivalents \| Level 1
Assets
Short-term investments	0	33,896
Commercial paper, not included in cash equivalents \| Level 2
Assets
Short-term investments	164,255	0
Commercial paper, not included in cash equivalents \| Level 3
Assets
Short-term investments	0	0
Auction rate securities
Assets
Long-term investments and other assets	967	1,016
Auction rate securities \| Level 1
Assets
Long-term investments and other assets	0	0
Auction rate securities \| Level 2
Assets
Long-term investments and other assets	0	0
Auction rate securities \| Level 3
Assets
Long-term investments and other assets	967	1,016
Interest rate swap
Assets
Long-term investments and other assets	13	16
Interest rate swap \| Level 1
Assets
Long-term investments and other assets	0	0
Interest rate swap \| Level 2
Assets
Long-term investments and other assets	13	16
Interest rate swap \| Level 3
Assets
Long-term investments and other assets	$ 0	$ 0

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

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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