Other Assets (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2016
Other Assets
Cash paid to support research activities and investment in private company		$ 3.5
Other assets related to investment in undisclosed private company		1.8
Other assets related to research and development expense		$ 1.7
Non-cash impairment charge on investments	$ 1.8

Amount of investment in equity security without readily determinable fair value.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117539-209714

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- Definition

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=109979856&loc=SL6284422-111562

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- References

No definition available.

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- Definition

The cash outflows from the purchase of net carrying value allocated to in-process research and development costs and materials acquired in a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585

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- Definition

The fair value of capitalized costs of a research and development nature that were acquired during the period in a transaction other than a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

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