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, 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 (42,438 shares in 2019, 42,872 shares in 2018, 43,650 shares in 2017)	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 (122,537 shares in 2019, 140,692 shares in 2018, 159,356 shares in 2017)	2,470	61	1,726	(103)	786
Cash dividends paid on common stock ($1.26 per share in 2019, $1.20 per share in 2018, $1.11 per share in 2017)	(32,199)			(32,199)
Stock dividend declared (719,515 shares in 2017)	0	899	24,061	(24,960)
Reclassification of certain deferred tax effects				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)	(14,015)					(14,015)
Issuance of common stock for dividend reinvestment plan (42,438 shares in 2019, 42,872 shares in 2018, 43,650 shares in 2017)	1,478	54	1,424
Purchase of common stock (66,467 shares in 2019 and 1,459,148 shares in 2018)	(47,193)				(47,193)
Stock compensation expense	2,317		2,317
Net issuance of common stock under employee stock plan (122,537 shares in 2019, 140,692 shares in 2018, 159,356 shares in 2017)	2,405	0	1,290	(128)	1,243
Cash dividends paid on common stock ($1.26 per share in 2019, $1.20 per share in 2018, $1.11 per share in 2017)	(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]
Net income	74,554			74,554
Other comprehensive income (loss)	54,464					54,464
Issuance of common stock for dividend reinvestment plan (42,438 shares in 2019, 42,872 shares in 2018, 43,650 shares in 2017)	1,445	53	1,392
Purchase of common stock (66,467 shares in 2019 and 1,459,148 shares in 2018)	(2,181)				(2,181)
Stock compensation expense	2,388		2,388
Net issuance of common stock under employee stock plan (122,537 shares in 2019, 140,692 shares in 2018, 159,356 shares in 2017)	1,592	0	468	(104)	1,228
Cash dividends paid on common stock ($1.26 per share in 2019, $1.20 per share in 2018, $1.11 per share in 2017)	(42,521)			(42,521)
Ending balance, net of tax at Dec. 31, 2019	$ 804,580	$ 47,360	$ 766,718	$ 80,274	$ (94,008)	$ 4,236