Investments and Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financial Assets
Total	$ 149,586	$ 156,093
Financial liabilities	1,238	2,571
Commercial paper
Financial Assets
Marketable investments	3,480	13,698
U.S. treasury
Financial Assets
Marketable investments	4,953	6,378
U.S. agency and government sponsored securities
Financial Assets
Marketable investments	5,300	7,690
U.S. states and municipalities
Financial Assets
Marketable investments		5,122
Corporate bonds
Financial Assets
Marketable investments	69,131	100,151
Commercial paper
Financial Assets
Cash equivalents		10,967
Money market funds
Financial Assets
Cash equivalents	66,722	12,087
Level 1
Financial Assets
Total	71,675	18,465
Financial liabilities	0	0
Level 1 \| Commercial paper
Financial Assets
Marketable investments	0	0
Level 1 \| U.S. treasury
Financial Assets
Marketable investments	4,953	6,378
Level 1 \| U.S. agency and government sponsored securities
Financial Assets
Marketable investments	0	0
Level 1 \| U.S. states and municipalities
Financial Assets
Marketable investments		0
Level 1 \| Corporate bonds
Financial Assets
Marketable investments	0	0
Level 1 \| Commercial paper
Financial Assets
Cash equivalents		0
Level 1 \| Money market funds
Financial Assets
Cash equivalents	66,722	12,087
Level 2
Financial Assets
Total	77,911	137,628
Financial liabilities	0	0
Level 2 \| Commercial paper
Financial Assets
Marketable investments	3,480	13,698
Level 2 \| U.S. treasury
Financial Assets
Marketable investments	0	0
Level 2 \| U.S. agency and government sponsored securities
Financial Assets
Marketable investments	5,300	7,690
Level 2 \| U.S. states and municipalities
Financial Assets
Marketable investments		5,122
Level 2 \| Corporate bonds
Financial Assets
Marketable investments	69,131	100,151
Level 2 \| Commercial paper
Financial Assets
Cash equivalents		10,967
Level 2 \| Money market funds
Financial Assets
Cash equivalents	0	0
Level 3
Financial Assets
Total	0	0
Financial liabilities	1,238	2,571
Level 3 \| Commercial paper
Financial Assets
Marketable investments	0	0
Level 3 \| U.S. treasury
Financial Assets
Marketable investments	0	0
Level 3 \| U.S. agency and government sponsored securities
Financial Assets
Marketable investments	0	0
Level 3 \| U.S. states and municipalities
Financial Assets
Marketable investments		0
Level 3 \| Corporate bonds
Financial Assets
Marketable investments	0	0
Level 3 \| Commercial paper
Financial Assets
Cash equivalents		0
Level 3 \| Money market funds
Financial Assets
Cash equivalents	0	0
Contingent Consideration Liability
Financial Assets
Financial liabilities	1,238	2,571
Contingent Consideration Liability \| Level 1
Financial Assets
Financial liabilities	0	0
Contingent Consideration Liability \| Level 2
Financial Assets
Financial liabilities	0	0
Contingent Consideration Liability \| Level 3
Financial Assets
Financial liabilities	$ 1,238	$ 2,571

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://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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