CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Series A Preferred Stock	Common Stock	Preferred Stock	Preferred Stock Series A Preferred Stock	Common Stock	Common Stock Common Stock	Surplus	Surplus Common Stock	Retained Earnings	Retained Earnings Common Stock	Accumulated Other Comprehensive Loss	Treasury Stock	Treasury Stock Common Stock
Beginning balance at Dec. 31, 2015	$ 2,207,091			$ 111,590		$ 88,626		$ 1,927,399		$ 125,171		$ (45,695)	$ 0
Beginning balance (in shares) at Dec. 31, 2015						253,788
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	168,146									168,146
Other comprehensive income (loss), net of tax	3,602											3,602
Stock issued	111,652					$ 3,362		106,265		(20)			2,045
Cash dividends declared on preferred stock	(7,188)									(7,188)
Cash dividends declared on common stock	(113,212)									(113,212)
Effect of stock incentive plan, net (in shares)						57
Effect of stock incentive plan, net	7,065					$ 365		10,737		(143)			(3,894)
Stock issued (in shares)						9,794
Ending balance at Dec. 31, 2016	2,377,156			111,590		$ 92,353		2,044,401		172,754		(42,093)	(1,849)
Ending balance (in shares) at Dec. 31, 2016						263,639
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	161,907									161,907
Reclassification due to the adoption of ASU No. 2018-02	(7,927)									7,927		(7,927)
Other comprehensive income (loss), net of tax	4,015											4,015
Stock issued		$ 98,101	$ 8,207		$ 98,101		$ 145		$ 4,658		$ (56)		3,460
Cash dividends declared on preferred stock	(9,449)									(9,449)
Cash dividends declared on common stock	(116,332)									(116,332)
Effect of stock incentive plan, net (in shares)						117
Effect of stock incentive plan, net	9,560					$ 229		11,297		(18)			(1,948)
Stock issued (in shares)							713
Ending balance at Dec. 31, 2017	2,533,165			209,691		$ 92,727		2,060,356		216,733		(46,005)	(337)
Ending balance (in shares) at Dec. 31, 2017						264,469
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	261,428									261,428
Other comprehensive income (loss), net of tax	(22,885)											(22,885)
Stock issued			738,211				$ 22,742		$ 715,121		0			$ 348
Cash dividends declared on preferred stock	(12,688)									(12,688)
Cash dividends declared on common stock			$ (146,346)								$ (146,346)
Effect of stock incentive plan, net (in shares)						1,955
Effect of stock incentive plan, net	17,180					$ 771		21,022		(2,415)			(2,198)
Stock issued (in shares)							65,007
Ending balance at Dec. 31, 2018	$ 3,350,454			$ 209,691		$ 116,240		$ 2,796,499		$ 299,642		$ (69,431)	$ (2,187)
Ending balance (in shares) at Dec. 31, 2018						331,431