Income Taxes - Deferred tax valuation (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Valuation Allowance, Deferred Tax Asset [Roll Forward]
Balance, beginning of year	$ 25,864	$ 18,829	$ 14,498
Other changes	2,264	7,035	4,331
Balance, end of year	$ 28,128	$ 25,864	$ 18,829

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant