Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands		Total	Preferred Stock	Common Stock		Additional Paid-In Capital		Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock at Cost
Beginning balance (in shares) at Dec. 31, 2013			0	31,917,385
Beginning balance at Dec. 31, 2013		$ 1,530,346	$ 0	$ 31,917		$ 1,178,284		$ 435,508	$ (16,491)	$ (98,872)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		69,445						69,445
Other comprehensive income		16,235							16,235
Cash dividends declared, $1.02 per share		(32,943)						(32,943)
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit		8,999				2,168				6,831
Common stock issued for acquisitions (in shares)				3,345,516
Common stock issued for acquisitions		214,665		$ 3,346		211,319
Stock issued		0				(6,080)				6,080
Share-based compensation cost		8,927				8,927
Ending balance (in shares) at Sep. 30, 2014			0	35,262,901
Ending balance at Sep. 30, 2014		1,815,674	$ 0	$ 35,263		1,394,618		472,010	(256)	(85,961)
Beginning balance (in shares) at Dec. 31, 2014			0	35,262,901
Beginning balance at Dec. 31, 2014		1,852,148	$ 0	$ 35,263		1,398,633		496,573	7,525	(85,846)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		98,437						98,437
Other comprehensive income		9,458							9,458
Cash dividends declared, $1.02 per share		(40,945)						(40,945)
Reclassification of treasury stock under the LBCA (in shares)	[1]			(1,809,497)
Reclassification of treasury stock under the LBCA		0		$ (1,809)	[1]	(84,037)	[1]			85,846	[1]
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit (in shares)				200,958
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit		1,748		$ 201		1,547				0
Common stock issued for acquisitions (in shares)				7,474,404
Common stock issued for acquisitions		474,753		$ 7,474		467,279
Preferred stock issued, shares			8,000
Stock issued		77,463	$ 8			77,455
Share-based compensation cost		10,139				10,139
Ending balance (in shares) at Sep. 30, 2015			8,000	41,128,766
Ending balance at Sep. 30, 2015		$ 2,483,201	$ 8	$ 41,129		$ 1,871,016		$ 554,065	$ 16,983	$ 0

[1] Effective January 1, 2015, companies incorporated in Louisiana became subject to the Louisiana Business Corporation Act (“LBCA”), which eliminates the concept of treasury stock and provides that shares reacquired by a company are to be treated as authorized but unissued. Refer to Note 1 for further discussion.