Share-based payments (Compensation Costs Related To Share-Based Payments) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock option compensation expense			$ 4,401	$ 4,852
Equity-classified share units	$ 4,138	$ 2,851	9,155	8,754
Liability-classified share units	2,123	589	1,938	829
Employee share purchase plan - employer contributions	636	567	1,835	1,692
Total compensation costs related to share based payments	8,568	5,660	17,329	16,127
Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock option compensation expense	$ 1,671	$ 1,653	$ 4,401	$ 4,852

Compensation Expense related to the company's contribution to employee stock purchase plan (ESPP).

No definition available.

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- Definition

Compensation expense representing accretion of the fair value of the contingently redeemable performance share units on the grant or modification date over the remaining service period.

+ References

No definition available.

+ Details

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- Definition

The expense that accounts for the value of liability-classified share units distributed to employees as compensation.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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Balance Type:	debit
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Amount of noncash expense for option under share-based payment arrangement.

+ References

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=121586364&loc=d3e3602-108585

+ Details

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- Details

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