Consolidated Statements of Changes in Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total Shareholders' Equity [Member]	Non-Controlling Interests [Member]
Balance, beginning of period (in shares) at Dec. 31, 2016		74,993			9,656
Balance, beginning of period at Dec. 31, 2016	$ 3,306,357	$ 4	$ 1,006,535	$ 2,823,334	$ (544,052)	$ (10,967)	$ 3,274,854	$ 31,503
Net income (loss)	177,530			176,503			176,503	1,027
Other comprehensive income (loss)	18,931					18,931	18,931
Stock options exercised (in shares)		41
Stock options exercised	1,977		1,977				1,977
Non-vested shares awarded, net (in shares)		55
Vesting of non-vested shares (in shares)					17
Vesting of non-vested shares	(1,389)				$ (1,389)		(1,389)
Share-based compensation	8,983		8,983				8,983
Cash dividends on common stock	(57,390)			(57,390)			(57,390)
Capital calls and distributions, net	(5,454)							(5,454)
Balance, end of period (in shares) at Jun. 30, 2017		75,089			9,673
Balance, end of period at Jun. 30, 2017	3,449,545	$ 4	1,017,495	2,942,447	$ (545,441)	7,964	3,422,469	27,076
Transition adjustment for unrealized gains and losses on equity securities	(2,709)			2,709		(2,709)
Balance, beginning of period, adjusted	3,518,334	$ 4	1,035,895	3,051,196	$ (552,845)	(38,883)	3,495,367	22,967
Balance, beginning of period (in shares) at Dec. 31, 2017		75,148			9,753
Balance, beginning of period at Dec. 31, 2017	3,518,334	$ 4	1,035,895	3,048,487	$ (552,845)	(36,174)	3,495,367	22,967
Net income (loss)	220,502			219,934			219,934	568
Other comprehensive income (loss)	(96,422)					(96,422)	(96,422)
Repurchase of common stock (in shares)					90
Repurchase of common stock	(8,408)				$ (8,408)		(8,408)
Stock options exercised (in shares)		46
Stock options exercised	2,426		2,426				2,426
Non-vested shares awarded, net (in shares)		120
Vesting of non-vested shares (in shares)					31
Vesting of non-vested shares	(2,870)				$ (2,870)		(2,870)
Share-based compensation	1,881		1,881				1,881
Cash dividends on common stock	(58,477)			(58,477)			(58,477)
Capital calls and distributions, net	(921)							(921)
Balance, end of period (in shares) at Jun. 30, 2018		75,314			9,874
Balance, end of period at Jun. 30, 2018	$ 3,576,045	$ 4	$ 1,040,202	$ 3,212,653	$ (564,123)	$ (135,305)	$ 3,553,431	$ 22,614