Computation of Earnings Per Common Share and Common Share Equivalent - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic earnings per common share & common share equivalents outstanding:
Net income (loss) attributable to common shareholders	$ 318,996	$ 301,620	$ 471,644	$ 454,463
Weighted average common shares outstanding - basic (in thousands of shares)	258,375	260,990	257,653	263,327
Basic earnings per common share & common share equivalents outstanding	$ 1.23	$ 1.16	$ 1.83	$ 1.73
Diluted earnings per common share & common share equivalents outstanding:
Weighted average common shares outstanding - basic (in thousands of shares)	258,375	260,990	257,653	263,327
Impact of share-based compensation	5,447	3,953	4,957	3,952
Weighted average common shares outstanding - diluted (in thousands of shares)	263,822	264,943	262,610	267,279
Diluted earnings per common share & common share equivalents outstanding	$ 1.21	$ 1.14	$ 1.80	$ 1.70
Dividends per ordinary share	$ 0.22	$ 0.22	$ 0.44	$ 0.44