Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Income taxes (Reconciliation of statutory income tax expense to provision for income taxes) (Details)

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Income taxes (Reconciliation of statutory income tax expense to provision for income taxes) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Income Tax Disclosure [Abstract]      
Statutory income tax rate 12.50% 12.50% 12.50%
Income tax expense at statutory income tax rate of 12.5% $ 167,580 $ 143,866 $ 154,484
Permanent differences (949) 1,016 23,737
Foreign rate differential 1,083 (803) (13,503)
Differences between statutory and actual income tax expense 134 213 10,234
Provision for income taxes $ 167,714 $ 144,079 $ 164,718