Equity and dividends (Schedule of Quarterly Dividends Declared and Paid) (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Fourth Quarter 2018 [Member]
Dividends Payable [Line Items]
Declaration date		Jan. 25, 2019
Dividend per share		$ 0.1800
Record date		Feb. 15, 2019
Total dividends		$ 19,568
Payment date		Mar. 08, 2019
Fourth Quarter 2019 [Member]
Dividends Payable [Line Items]
Declaration date	Jan. 24, 2020
Dividend per share	$ 0.2000
Record date	Feb. 14, 2020
Total dividends	$ 21,905
Payment date	Mar. 06, 2020
First Quarter 2020 [Member]
Dividends Payable [Line Items]
Declaration date	May 06, 2020
Dividend per share	$ 0.2000
Record date	May 27, 2020
Total dividends	$ 21,681
Payment date	Jun. 17, 2020
Second Quarter 2020 [Member]
Dividends Payable [Line Items]
Declaration date	Aug. 05, 2020
Dividend per share	$ 0.2200
Record date	Aug. 26, 2020
Total dividends	$ 24,053
Payment date	Sep. 16, 2020
First Quarter 2019 [Member]
Dividends Payable [Line Items]
Declaration date		May 08, 2019
Dividend per share		$ 0.1800
Record date		May 29, 2019
Total dividends		$ 19,592
Payment date		Jun. 19, 2019
Second Quarter 2019 [Member]
Dividends Payable [Line Items]
Declaration date		Aug. 08, 2019
Dividend per share		$ 0.2000
Record date		Aug. 28, 2019
Total dividends		$ 21,631
Payment date		Sep. 18, 2019

Aggregate dividends declared during the period for each share of common stock outstanding.

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586

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Amount of paid and unpaid cash, stock, and paid-in-kind (PIK) dividends declared, for example, but not limited to, common and preferred stock.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6957935&loc=d3e64057-112817

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Date the dividend to be paid was declared, in CCYY-MM-DD format.

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Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

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