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Income taxes - Changes in Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, valuation allowance	$ 839,082	$ 768,764	$ 748,283
Remeasurement of deferred tax assets	(205,150)	0	0
Release of valuation allowance	0	(6,007)	0
Other change in valuation allowance	(26,119)	76,325	20,481
Balance, valuation allowance	$ 607,813	$ 839,082	$ 768,764

X

- Definition

Valuation Allowance, Deferred Tax Asset, Release of Valuation Allowance

+ References

No definition available.

+ Details

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X

- Definition

Valuation Allowance, Deferred Tax Asset, Remeasurement Due To Tax Cuts & Jobs Act

+ References

No definition available.

+ Details

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X

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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X

- Definition

Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e32123-109318

+ Details

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X

- Definition

Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

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