Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Deferred Compensation [Member]	Accumulated Other Comprehensive Earnings (Losses) [Member]
Beginning Balance at Dec. 31, 2013	$ 587,647	$ 320	$ 302,991	$ 273,972	$ (5,490)	$ 5,490	$ 10,364
Beginning Balance, Shares at Dec. 31, 2013		31,992,497
Treasury Stock, Beginning Balance, Shares at Dec. 31, 2013					(269,467)
NET EARNINGS	89,559			89,559
Stock option exercises	1,437	$ 1	1,436
Stock option exercises, Shares		74,664
Cash dividends declared	(35,233)			(35,233)
Minimum liability pension adjustment, net of related income taxes	1,651						1,651
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes	35,474						35,474
Additional tax benefit related to directors' deferred compensation plan	$ 293		293
Shares purchased in connection with directors' deferred compensation plan, net					$ (388)	388
Shares purchased in connection with directors' deferred compensation plan, net, Shares	0				8,038
Stock option expense	$ 709		709
Two-for-one stock split in the form of 100% stock dividend		$ 320		(320)
Two-for-one stock split in the form of a 100% stock dividend, Shares		32,022,760			(268,134)
Ending Balance at Dec. 31, 2014	681,537	$ 641	305,429	327,978	$ (5,878)	5,878	47,489
Ending Balance, Shares at Dec. 31, 2014		64,089,921
Treasury Stock, Ending Balance, Shares at Dec. 31, 2014					(529,563)
NET EARNINGS	100,381			100,381
Stock issued in acquisition of FBC Bancshares, Inc.	59,648	$ 18	59,630
Stock issued in acquisition of FBC Bancshares, Inc., Shares		1,755,374
Stock option exercises	1,545	$ 1	1,544
Stock option exercises, Shares		105,121
Restricted Stock grant	1,350		1,350
Restricted stock grant, Shares		39,818
Cash dividends declared	(40,353)			(40,353)
Minimum liability pension adjustment, net of related income taxes	(1,291)						(1,291)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes	1,197						1,197
Additional tax benefit related to directors' deferred compensation plan	$ 328		328
Shares purchased in connection with directors' deferred compensation plan, net					$ (418)	418
Shares purchased in connection with directors' deferred compensation plan, net, Shares	0				8,912
Stock option expense	$ 644		644
Ending Balance at Dec. 31, 2015	$ 804,986	$ 660	368,925	388,006	$ (6,296)	6,296	47,395
Ending Balance, Shares at Dec. 31, 2015		65,990,234
Treasury Stock, Ending Balance, Shares at Dec. 31, 2015	(520,651)				(520,651)
NET EARNINGS	$ 104,774			104,774
Stock option exercises	1,260	$ 1	1,259
Stock option exercises, Shares		82,871
Restricted Stock grant	809		809
Restricted stock grant, Shares		21,590
Cash dividends declared	(46,246)			(46,246)
Minimum liability pension adjustment, net of related income taxes	917						917
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes	(29,867)						(29,867)
Additional tax benefit related to directors' deferred compensation plan	$ 370		370
Shares purchased in connection with directors' deferred compensation plan, net					$ (375)	375
Shares purchased in connection with directors' deferred compensation plan, net, Shares	0				13,242
Stock option expense	$ 882		882
Ending Balance at Dec. 31, 2016	$ 837,885	$ 661	$ 372,245	$ 446,534	$ (6,671)	$ 6,671	$ 18,445
Ending Balance, Shares at Dec. 31, 2016		66,094,695
Treasury Stock, Ending Balance, Shares at Dec. 31, 2016	(507,409)				(507,409)