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, 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		25,126				25,126
Other comprehensive income		9,792					9,792
Cash dividends declared, $0.34 per share		(12,981)				(12,981)
Reclassification of treasury stock under the LBCA (in shares)	[1]			(1,809,497)
Reclassification of treasury stock under the LBCA (1)	[1]	0		$ (1,810)	(84,036)			85,846
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit (in shares)				132,969
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit		789		$ 133	656			0
Common stock issued for acquisitions (in shares)				4,592,047
Common stock issued for acquisitions		289,504		$ 4,592	284,912
Share-based compensation cost		2,952			2,952
Ending balance (in shares) at Mar. 31, 2015			0	38,178,420
Ending balance at Mar. 31, 2015		2,167,330	$ 0	$ 38,178	1,603,117	508,718	17,317	0
Beginning balance (in shares) at Dec. 31, 2015			8,000	41,139,537
Beginning balance at Dec. 31, 2015		2,498,835	$ 76,812	$ 41,140	1,797,982	584,486	(1,585)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		42,769				42,769
Other comprehensive income		21,193					21,193
Cash dividends declared, $0.34 per share		(14,019)				(14,019)
Preferred stock dividends		(2,576)				(2,576)
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit (in shares)				92,323
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit		(2,163)		$ 92	(2,255)			0
Share-based compensation cost		3,870			3,870
Ending balance (in shares) at Mar. 31, 2016			8,000	41,231,860
Ending balance at Mar. 31, 2016		$ 2,547,909	$ 76,812	$ 41,232	$ 1,799,597	$ 610,660	$ 19,608	$ 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, Summary of Significant Accounting Policies, in the Annual Report on Form 10-K for the year ended December 31, 2015, for further discussion.