CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common Stock	Paid In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)
Beginning balance, net of tax at Dec. 31, 2015	$ 444,062	$ 34,832	$ 424,078	$ 41,527	$ (37,692)	$ (18,683)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	49,349			49,349
Other comprehensive income (loss)	(19,810)					(19,810)
Issuance of common stock for dividend reinvestment plan (42,872 shares in 2018, 43,650 shares in 2017, 44,575 shares in 2016)	1,411	56	1,355
Net issuance of common stock (2,185,000 shares in 2016)	75,992	2,731	73,261
Tax benefit related to stock awards	332		332
Purchase of common stock (1,459,148 shares in 2018, 443,426 shares in 2016)	(10,199)				(10,199)
Stock compensation expense	1,541		1,541
Net issuance of common stock under employee stock plan (140,692 shares in 2018, 159,356 shares in 2017, 108,255 shares in 2016)	1,559	136	1,473	(50)
Cash dividends paid on common stock ($1.20 per share in 2018, $1.11 per share in 2017, $1.01 per share in 2016)	(25,963)			(25,963)
Stock dividend declared (719,515 shares in 2017, 1,252,353 shares in 2016)	0	1,565	33,200	(34,765)
Ending balance, net of tax at Dec. 31, 2016	518,274	39,320	535,240	30,098	(47,891)	(38,493)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	54,312			54,312
Other comprehensive income (loss)	7,898					7,898
Issuance of common stock for dividend reinvestment plan (42,872 shares in 2018, 43,650 shares in 2017, 44,575 shares in 2016)	1,483	54	1,429
Net issuance of common stock in connection with the acquisition of Diboll State Bancshares, Inc. (5,534,925 shares)	200,087	6,919	193,168
Stock compensation expense	1,815		1,815
Net issuance of common stock under employee stock plan (140,692 shares in 2018, 159,356 shares in 2017, 108,255 shares in 2016)	2,470	61	1,726	(103)	786
Cash dividends paid on common stock ($1.20 per share in 2018, $1.11 per share in 2017, $1.01 per share in 2016)	(32,199)			(32,199)
Stock dividend declared (719,515 shares in 2017, 1,252,353 shares in 2016)	0	899	24,061	(24,960)
Reclassification of certain deferred tax effects	0			5,703		(5,703)
Ending balance, net of tax at Dec. 31, 2017	754,140	47,253	757,439	32,851	(47,105)	(36,298)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	74,138			74,138
Other comprehensive income (loss)	(13,930)					(13,930)
Issuance of common stock for dividend reinvestment plan (42,872 shares in 2018, 43,650 shares in 2017, 44,575 shares in 2016)	1,478	54	1,424
Purchase of common stock (1,459,148 shares in 2018, 443,426 shares in 2016)	(47,193)				(47,193)
Stock compensation expense	2,317		2,317
Net issuance of common stock under employee stock plan (140,692 shares in 2018, 159,356 shares in 2017, 108,255 shares in 2016)	2,405	0	1,290	(128)	1,243
Cash dividends paid on common stock ($1.20 per share in 2018, $1.11 per share in 2017, $1.01 per share in 2016)	(41,979)			(41,979)
Ending balance, net of tax at Dec. 31, 2018	731,291	$ 47,307	$ 762,470	64,797	$ (93,055)	$ (50,228)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of ASU 2016-01	$ (85)			$ (85)