Consolidated Statements of Changes in Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Preferred Stock	Common Stock	Preferred Stock	Preferred Stock Preferred Stock	Common Stock	Common Stock Common Stock	Surplus	Surplus Common Stock	Retained Earnings	Retained Earnings Preferred Stock	Retained Earnings Common Stock	Accumulated Other Comprehensive Loss	Treasury Stock	Treasury Stock Common Stock
Beginning balance at Dec. 31, 2013	$ 1,541,040			$ 0		$ 69,941		$ 1,403,375		$ 106,340			$ (38,252)	$ (364)
Beginning balance, shares at Dec. 31, 2013						199,593
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	116,172									116,172
Other comprehensive loss, net of tax	(4,243)												(4,243)
Cash dividends declared on stock	(91,581)									(91,581)
Effect of stock incentive plan, net	5,806					$ 234		6,269		(83)				(614)
Effect of stock incentive plan, net, shares						1,299
Stock issued	295,823					$ 10,897		284,108		(3)				821
Stock issued, shares						31,219
Ending balance at Dec. 31, 2014	1,863,017			0		$ 81,072		1,693,752		130,845			(42,495)	(157)
Ending balance, 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)
Cash dividends declared on stock		$ (3,813)	$ (104,753)								$ (3,813)	$ (104,753)
Effect of stock incentive plan, net	4,715					$ 190		7,153		(30)				(2,598)
Effect of stock incentive plan, net, shares						500
Stock issued		111,590	236,578		$ 111,590		$ 7,364		$ 226,494			(35)		2,755
Stock issued, shares							21,177
Ending balance at Dec. 31, 2015	2,207,091			111,590		$ 88,626		1,927,399		125,171			(45,695)	0
Ending balance, 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
Cash dividends declared on stock		$ (7,188)	(113,212)								$ (7,188)	(113,212)
Effect of stock incentive plan, net	7,065					$ 365		10,737		(143)				(3,894)
Effect of stock incentive plan, net, shares						57
Stock issued			$ 111,652				$ 3,362		$ 106,265			$ (20)			$ 2,045
Stock issued, 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, shares at Dec. 31, 2016						263,639