Consolidated Statements of Shareholders' Equity (USD $) In Thousands, except Share data		Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Beginning balance at Dec. 31, 2013		$ 1,530,346	$ 31,917	$ 1,178,284	$ 435,508	$ (16,491)	$ (98,872)
Beginning balance, Shares at Dec. 31, 2013			31,917,385
Net income		22,336			22,336
Other comprehensive income		10,315				10,315
Cash dividends declared, $0.34 per share		(10,214)			(10,214)
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit		6,879		1,862			5,017
Common stock issued for recognition and retention plans				(5,836)			5,836
Share-based compensation cost		2,835		2,835
Ending balance at Mar. 31, 2014		1,562,497	31,917	1,177,145	447,630	(6,176)	(88,019)
Ending balance, Shares at Mar. 31, 2014			31,917,385
Beginning balance at Dec. 31, 2014		1,852,148	35,263	1,398,633	496,573	7,525	(85,846)
Beginning balance, Shares at Dec. 31, 2014			35,262,901
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	[1]		(1,810)	(84,036)			85,846
Reclassification of treasury stock under the LBCA, Shares	[1]		(1,809,497)
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit		789	133	656
Common stock issued under incentive plans, net of shares surrendered in payment, including tax benefit, Shares			132,969
Common stock issued for acquisitions		289,504	4,592	284,912
Common stock issued for acquisitions, Shares		3,083,229	4,592,047
Share-based compensation cost		2,952		2,952
Ending balance at Mar. 31, 2015		$ 2,167,330	$ 38,178	$ 1,603,117	$ 508,718	$ 17,317
Ending balance, Shares at Mar. 31, 2015			38,178,420

[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.