CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Parent [Member]	Preferred shares [Member]	Common shares (par value) [Member]	Additional paid-in capital [Member]	Unrealized gains (losses) on available for sale investments, net of tax [Member]	Cumulative foreign currency translation adjustments, net of tax [Member]	Accumulated other comprehensive income [Member]	Retained earnings [Member]	Treasury shares, at cost [Member]	Noncontrolling interest [Member]
Total shareholders' equity at Dec. 31, 2013			$ 627,843	$ 2,174	$ 2,240,125	$ 124,945	$ (7,120)	$ 117,825	$ 5,062,706	$ (2,232,711)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued				15	2,549
Cost of treasury shares reissued					(11,524)					11,524
Stock options exercised					2,134
Share-based compensation expense					27,800
Unrealized gains (losses) arising during the period, net of reclassification adjustment	$ 148,390					148,390
Non-credit portion of OTTI losses	0					0
Foreign currency translation adjustment	6,449						6,449
Net income	350,729								350,729
Amounts attributable to noncontrolling interests	(2,795)								(2,795)
Preferred share dividends									(20,044)
Common share dividends									(59,397)
Shares repurchased for treasury										(318,082)
Total shareholders' equity at Jun. 30, 2014	6,008,505	$ 5,955,710	627,843	2,189	2,261,084	273,335	(671)	272,664	5,331,199	(2,539,269)	$ 52,795
Total shareholders' equity at Dec. 31, 2014	5,879,940		627,843	2,191	2,285,016	(28,192)	(17,382)	(45,574)	5,715,504	(2,763,859)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued				10	2,605
Cost of treasury shares reissued					(17,451)					17,451
Stock options exercised					560
Share-based compensation expense					15,042
Unrealized gains (losses) arising during the period, net of reclassification adjustment	(23,268)					(23,268)
Non-credit portion of OTTI losses	0					0
Foreign currency translation adjustment	(9,225)						(9,225)
Net income	239,197								239,197
Amounts attributable to noncontrolling interests	0								0
Preferred share dividends									(20,044)
Common share dividends									(59,510)
Shares repurchased for treasury										(17,930)
Total shareholders' equity at Jun. 30, 2015	$ 5,948,558	$ 5,948,558	$ 627,843	$ 2,201	$ 2,285,772	$ (51,460)	$ (26,607)	$ (78,067)	$ 5,875,147	$ (2,764,338)	$ 0