Consolidated Statements of Changes in Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Series A Preferred Stock	Common Stock	Series B Preferred Stock	Preferred Stock	Preferred Stock Series A Preferred Stock	Preferred Stock Series B 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, 2014	$ 1,863,017				$ 0			$ 81,072		$ 1,693,752		$ 130,845		$ (42,495)	$ (157)
Beginning balance (in shares) at Dec. 31, 2014								232,111
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	102,957											102,957
Other comprehensive loss, net of tax	(3,200)													(3,200)
Stock issued	236,578	$ 111,590				$ 111,590		$ 7,364		226,494		(35)			2,755
Stock issued (in shares)								21,177
Cash dividends declared on preferred stock	(3,813)											(3,813)
Cash dividends declared on common stock	(104,753)											(104,753)
Effect of stock incentive plan, net (in shares)								500
Effect of stock incentive plan, net	4,715							$ 190		7,153		(30)			(2,598)
Ending balance at Dec. 31, 2015	2,207,091				111,590			$ 88,626		1,927,399		125,171		(45,695)	0
Ending balance (in shares) at Dec. 31, 2015								253,788
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	168,146											168,146
Other comprehensive loss, net of tax	3,602													3,602
Stock issued			$ 111,652						$ 3,362		$ 106,265		$ (20)		2,045
Stock issued (in shares)									9,794
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)
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]
Reclassification due to the adoption of ASU No. 2018-02	0											7,927		(7,927)
Net income	161,907											161,907
Other comprehensive loss, net of tax	4,015													4,015
Stock issued			8,207	$ 98,101			$ 98,101		$ 145		$ 4,658		(56)			$ 3,460
Stock issued (in shares)									713
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)
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