Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Surplus	Accumulated Other Comprehensive Income (Loss)	Undivided Profits	Hardeman County Investment Company, Inc.	Hardeman County Investment Company, Inc. Common Stock	Hardeman County Investment Company, Inc. Surplus	OKSB Merger	OKSB Merger Common Stock	OKSB Merger Surplus	First Texas Merger	First Texas Merger Common Stock	First Texas Merger Surplus
Balance at Dec. 31, 2016		$ 1,151,111	$ 626	$ 711,663	$ (15,212)	$ 454,034
Comprehensive income		49,075			3,890	45,185
Stock issued for employee stock purchase plan		618		618
Stock-based compensation plans, net		6,531	2	6,529
Stock issued for acquisition							$ 42,638	$ 16	$ 42,622
Dividends on common stock	[1]	(15,897)	0	0	0	(15,897)
Balance at Jun. 30, 2017		1,234,076	644	761,432	(11,322)	483,322
Comprehensive income		44,829			(2,926)	47,755
Reclassify stranded tax effects due to 2017 tax law changes		0			(3,016)	3,016
Stock-based compensation plans, net		6,410	1	6,409
Stock issued for acquisition										$ 431,398	$ 145	$ 431,253	$ 387,070	$ 130	$ 386,940
Dividends on common stock	[1]	(19,219)	0	0	0	(19,219)
Balance at Dec. 31, 2017		2,084,564	920	1,586,034	(17,264)	514,874
Comprehensive income		81,955	0	0	(22,919)	104,874
Stock issued for employee stock purchase plan		1,026	0	1,026	0	0
Stock-based compensation plans, net		7,285	3	7,282	0	0
Dividends on common stock	[1]	(27,922)	0	0	0	(27,922)
Balance at Jun. 30, 2018		$ 2,146,908	$ 923	$ 1,594,342	$ (40,183)	$ 591,826

[1] All share and per share amounts have been restated to reflect the effect of the two-for-one stock split on February 8, 2018.