Fair Value (Details) - Fair value, recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets
Total cash and cash equivalents	$ 128,435	$ 93,519
Total marketable securities	425,177	421,703
Total financial assets	553,612	515,222
Cash [Member]
Assets
Total cash and cash equivalents	127,672	93,384
Money market funds [Member]
Assets
Total cash and cash equivalents	763	135
Commercial paper and corporate bonds [Member]
Assets
Total marketable securities	387,603	388,636
U.S. government agency debt securities [Member]
Assets
Total marketable securities	37,574	33,067
Contingent Consideration [Member]
Liabilities
Contingent consideration - short-term	3,985	0
Contingent consideration - long-term	1,867	0
Total financial liabilities	5,852	0
Level 1 [Member]
Assets
Total cash and cash equivalents	128,435	93,519
Total marketable securities	0	0
Total financial assets	128,435	93,519
Level 1 [Member] | Cash [Member]
Assets
Total cash and cash equivalents	127,672	93,384
Level 1 [Member] | Money market funds [Member]
Assets
Total cash and cash equivalents	763	135
Level 1 [Member] | Commercial paper and corporate bonds [Member]
Assets
Total marketable securities	0	0
Level 1 [Member] | U.S. government agency debt securities [Member]
Assets
Total marketable securities	0	0
Level 1 [Member] | Contingent Consideration [Member]
Liabilities
Contingent consideration - short-term	0	0
Contingent consideration - long-term	0	0
Total financial liabilities	0	0
Level 2 [Member]
Assets
Total cash and cash equivalents	0	0
Total marketable securities	425,177	421,703
Total financial assets	425,177	421,703
Level 2 [Member] | Cash [Member]
Assets
Total cash and cash equivalents	0	0
Level 2 [Member] | Money market funds [Member]
Assets
Total cash and cash equivalents	0	0
Level 2 [Member] | Commercial paper and corporate bonds [Member]
Assets
Total marketable securities	387,603	388,636
Level 2 [Member] | U.S. government agency debt securities [Member]
Assets
Total marketable securities	37,574	33,067
Level 2 [Member] | Contingent Consideration [Member]
Liabilities
Contingent consideration - short-term	0	0
Contingent consideration - long-term	0	0
Total financial liabilities	0	0
Level 3 [Member]
Assets
Total cash and cash equivalents	0	0
Total marketable securities	0	0
Total financial assets	0	0
Level 3 [Member] | Cash [Member]
Assets
Total cash and cash equivalents	0	0
Level 3 [Member] | Money market funds [Member]
Assets
Total cash and cash equivalents	0	0
Level 3 [Member] | Commercial paper and corporate bonds [Member]
Assets
Total marketable securities	0	0
Level 3 [Member] | U.S. government agency debt securities [Member]
Assets
Total marketable securities	0	0
Level 3 [Member] | Contingent Consideration [Member]
Liabilities
Contingent consideration - short-term	3,985	0
Contingent consideration - long-term	1,867	0
Total financial liabilities	$ 5,852	$ 0