Fair Value Measurements (Assets And Liabilities Measured At Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets
Total	$ 971,597	$ 713,072
Liabilities
Long-term debt	39,436	42,004
Interest rate swap	666
Contingent purchase consideration		273
Total	40,102	42,277
Level 1
Assets
Total	269,955	421,003
Liabilities
Long-term debt	0	0
Interest rate swap	0
Contingent purchase consideration		0
Total	0	0
Level 2
Assets
Total	701,642	291,477
Liabilities
Long-term debt	39,436	42,004
Interest rate swap	666
Contingent purchase consideration		0
Total	40,102	42,004
Level 3
Assets
Total	0	592
Liabilities
Long-term debt	0	0
Interest rate swap	0
Contingent purchase consideration		273
Total	0	273
Money market fund deposits and term deposits
Assets
Cash equivalents	269,955	155,080
Money market fund deposits and term deposits \| Level 1
Assets
Cash equivalents	269,955	155,080
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
Commercial paper
Assets
Cash equivalents	126,563	54,712
Commercial paper \| Level 1
Assets
Cash equivalents	0	0
Commercial paper \| Level 2
Assets
Cash equivalents	126,563	54,712
Commercial paper \| Level 3
Assets
Cash equivalents	0	0
Corporate bonds
Assets
Cash equivalents	25,142
Short-term investments	183,827	259,422
Corporate bonds \| Level 1
Assets
Cash equivalents	0
Short-term investments	0	259,422
Corporate bonds \| Level 2
Assets
Cash equivalents	25,142
Short-term investments	183,827	0
Corporate bonds \| Level 3
Assets
Cash equivalents	0
Short-term investments	0	0
U.S. Treasury and agency obligations
Assets
Cash equivalents	11,799
Short-term investments	38,144
U.S. Treasury and agency obligations \| Level 1
Assets
Cash equivalents	0
Short-term investments	0
U.S. Treasury and agency obligations \| Level 2
Assets
Cash equivalents	11,799
Short-term investments	38,144
U.S. Treasury and agency obligations \| Level 3
Assets
Cash equivalents	0
Short-term investments	0
Commercial paper
Assets
Short-term investments	316,167	236,752
Commercial paper \| Level 1
Assets
Short-term investments	0	0
Commercial paper \| Level 2
Assets
Short-term investments	316,167	236,752
Commercial paper \| Level 3
Assets
Short-term investments	$ 0	0
Certificate of deposit
Assets
Short-term investments		6,501
Certificate of deposit \| Level 1
Assets
Short-term investments		6,501
Certificate of deposit \| Level 2
Assets
Short-term investments		0
Certificate of deposit \| Level 3
Assets
Short-term investments		0
Auction rate securities
Assets
Long-term investments and other assets		592
Auction rate securities \| Level 1
Assets
Long-term investments and other assets		0
Auction rate securities \| Level 2
Assets
Long-term investments and other assets		0
Auction rate securities \| Level 3
Assets
Long-term investments and other assets		592
Interest rate swap
Assets
Long-term investments and other assets		13
Interest rate swap \| Level 1
Assets
Long-term investments and other assets		0
Interest rate swap \| Level 2
Assets
Long-term investments and other assets		13
Interest rate swap \| Level 3
Assets
Long-term investments and other assets		$ 0

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