Income taxes - Reconciliation of statutory to effective income tax rate (Details)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal Statutory Rate	35.00%	35.00%	35.00%
Permanent differences	7.70%	1.90%	4.30%
State taxes, net of Federal benefit	6.10%	(16.00%)	(6.20%)
Rate change - foreign	(4.20%)	0.00%	0.00%
Foreign earnings taxed at different rates than U.S.	(13.50%)	3.00%	(1.30%)
Valuation allowance	(27.50%)	(56.60%)	(26.00%)
Changes in uncertain tax reserves	(1.00%)	(4.20%)	0.60%
Other	(3.70%)	14.30%	6.40%
Effective tax rate	(1.10%)	(22.60%)	12.80%

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32698-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(2))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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-Publisher FASB
-Name Accounting Standards Codification
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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32687-109319

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-Publisher FASB
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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to income tax contingencies. Includes, but not limited to, domestic tax contingency, foreign tax contingency, state and local tax contingency, and other contingencies.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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