Nature of operations and summary of significant accounting policies (Other) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2018
Other Income and Expenses [Abstract]
Restructuring	$ 0			$ 425
Subleases	402			1,208
Total other expense	$ 402	$ 0	$ 0	$ 1,633

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration