Patent License Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
Jan. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Finite-Lived Intangible Assets, Net [Abstract]
Payment in connection with patent licensing agreement	$ 9,700
Capitalized license fees		$ 7,557		$ 7,800
Useful life (years)		7 years 9 months		8 years
Amortization of intangible assets		$ 243	$ 189

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

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