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

Earnings per share (Computations of ordinary shares outstanding, excluding nonvested restricted stock) (Details)

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Earnings per share (Computations of ordinary shares outstanding, excluding nonvested restricted stock) (Details) - shares
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Earnings Per Share [Abstract]      
Ordinary share issued (in shares) 167,847,345 187,847,345 203,411,207
Treasury shares (in shares) (14,855,244) (11,600,191) (3,069,003)
Ordinary shares outstanding (in shares) 152,992,101 176,247,154 200,342,204
Unvested restricted stock (in shares) (3,007,752) (3,426,810) (3,030,724)
Ordinary shares outstanding, excluding shares of unvested restricted stock (in shares) 149,984,349 172,820,344 197,311,480