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)	88,664			88,356			88,356	308
Other comprehensive income (loss)	5,746					5,746	5,746
Stock options exercised (in shares)		27
Stock options exercised	1,222		1,222				1,222
Non-vested shares awarded, net (in shares)		61
Vesting of non-vested shares (in shares)					17
Vesting of non-vested shares	(1,389)				$ (1,389)		(1,389)
Share-based compensation	1,603		1,603				1,603
Cash dividends on common stock	(28,648)			(28,648)			(28,648)
Capital calls and distributions, net	(2,661)							(2,661)
Balance, end of period (in shares) at Mar. 31, 2017		75,081			9,673
Balance, end of period at Mar. 31, 2017	3,370,894	$ 4	1,009,360	2,883,042	$ (545,441)	(5,221)	3,341,744	29,150
Balance, beginning of period, adjusted	3,518,334	$ 4	1,035,895	3,051,196	$ (552,845)	(38,883)	3,495,367	22,967
Transition adjustment for unrealized gains and losses on equity securities				2,709		(2,709)
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)	105,347			105,562			105,562	(215)
Other comprehensive income (loss)	(72,308)					(72,308)	(72,308)
Repurchase of common stock (in shares)					83
Repurchase of common stock	(7,584)				$ (7,584)		(7,584)
Stock options exercised (in shares)		43
Stock options exercised	2,274		2,274				2,274
Non-vested shares awarded, net (in shares)		127
Vesting of non-vested shares (in shares)					23
Vesting of non-vested shares	(2,172)				$ (2,172)		(2,172)
Share-based compensation	3,073		3,073				3,073
Cash dividends on common stock	(29,183)			(29,183)			(29,183)
Capital calls and distributions, net	(439)							(439)
Balance, end of period (in shares) at Mar. 31, 2018		75,318			9,859
Balance, end of period at Mar. 31, 2018	3,517,342	$ 4	$ 1,041,242	$ 3,127,575	$ (562,601)	$ (111,191)	$ 3,495,029	$ 22,313
Transition adjustment for unrealized gains and losses on equity securities	$ (2,709)