Shareholders' equity, net - Dividends declared and paid (Details) - USD ($)
$ / shares in Units, $ in Thousands

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (28,598)

$ (28,420)

$ (28,135)

Dividend 2019 [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

(22,098)

Dividend 2019 [Member] | Annual General Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

(15,240)

Dividend 2019 [Member] | Directors Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

(6,858)

Dividends 2018 [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

(22,860)

Dividends 2018 [Member] | Annual General Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

(7,621)

Dividends 2018 [Member] | Directors Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

(15,239)

Dividends 2017 [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

(22,099)

Dividends 2017 [Member] | Annual General Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

(14,479)

Dividends 2017 [Member] | Directors Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

(7,620)

Ordinary shares [member] | Dividend 2019 [Member] | Annual General Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (16,538)

Dividends paid, ordinary shares per share

$ 0.06

Ordinary shares [member] | Dividend 2019 [Member] | Directors Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (7,442)

Dividends paid, ordinary shares per share

$ 0.03

Ordinary shares [member] | Dividends 2018 [Member] | Annual General Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (8,269)

Dividends paid, ordinary shares per share

$ 0.030

Ordinary shares [member] | Dividends 2018 [Member] | Directors Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (16,538)

Dividends paid, ordinary shares per share

$ 0.060

Ordinary shares [member] | Dividends 2017 [Member] | Annual General Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (15,711)

Dividends paid, ordinary shares per share

$ 0.06

Ordinary shares [member] | Dividends 2017 [Member] | Directors Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (8,269)

Dividends paid, ordinary shares per share

$ 0.03

Treasury shares [member] | Dividend 2019 [Member] | Annual General Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (1,298)

Treasury shares [member] | Dividend 2019 [Member] | Directors Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (584)

Treasury shares [member] | Dividends 2018 [Member] | Annual General Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (648)

Treasury shares [member] | Dividends 2018 [Member] | Directors Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (1,299)

Treasury shares [member] | Dividends 2017 [Member] | Annual General Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (1,232)

Treasury shares [member] | Dividends 2017 [Member] | Directors Meeting [Member]

Disclosure of Shareholders' equity, net [Line Items]

Dividends declared and paid

$ (649)