CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Parent [Member]	Preferred shares [Member]	Common shares (par value) [Member]	Additional paid-in capital [Member]	Accumulated other comprehensive income (loss) [Member]	Unrealized gains (losses) on available for sale investments, net of tax [Member]	Cumulative foreign currency translation adjustments, net of tax [Member]	Retained earnings [Member]	Treasury shares, at cost [Member]
Total shareholders’ equity at Dec. 31, 2015			$ 627,843	$ 2,202	$ 2,241,388	$ (188,465)	$ (149,585)	$ (38,880)	$ 6,194,353	$ (3,010,439)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased			(2,843)
Shares issued				4	1,779
Cost of treasury shares reissued					(15,008)					16,392
Shares repurchased for treasury					60,000					(196,011)
Share-based compensation expense					8,373
Unrealized gains arising during the period, net of reclassification adjustment	$ 197,915						197,915
Foreign currency translation adjustment	8,196							8,196
Net income	48,386								48,386
Preferred share dividends									(9,969)
Common share dividends									(33,838)
Total shareholders’ equity at Mar. 31, 2016		$ 5,950,259	625,000	2,206	2,296,533	17,646	48,330	(30,684)	6,198,932	(3,190,058)
Total shareholders’ equity at Dec. 31, 2016	6,272,370		1,126,074	2,206	2,299,857	(121,841)	(82,323)	(39,518)	6,527,627	(3,561,553)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased			0
Shares issued				0	0
Cost of treasury shares reissued					(37,363)					38,248
Shares repurchased for treasury					0					(151,242)
Share-based compensation expense					14,177
Unrealized gains arising during the period, net of reclassification adjustment	92,671						92,671
Foreign currency translation adjustment	29,869							29,869
Net income	19,855								19,855
Preferred share dividends									(14,841)
Common share dividends									(33,379)
Total shareholders’ equity at Mar. 31, 2017	$ 6,230,365	$ 6,230,365	$ 1,126,074	$ 2,206	$ 2,276,671	$ 699	$ 10,348	$ (9,649)	$ 6,499,262	$ (3,674,547)