Consolidated Statements of Stockholders' Equity (Parentheticals)		12 Months Ended
		Dec. 31, 2019 $ / shares shares	Dec. 31, 2018 $ / shares shares	Dec. 31, 2017 $ / shares shares
Stock issued for employee stock purchase plan, shares (in shares)		60,413	39,782	26,002	[1]
Stock issued for compensation plans, shares (in shares)		261,200	278,743	359,286	[1]
Stock repurchases (in shares)		390,000	0
Cash dividends, per share (in dollars per share) | $ / shares		$ 0.64	$ 0.60	$ 0.50	[1]
Hardeman County Investment Company, Inc.
Stock issued for acquisition, shares (in shares)	[1]			1,599,940
OKSB Merger
Stock issued for acquisition, shares (in shares)	[1]			14,488,604
First Texas Merger
Stock issued for acquisition, shares (in shares)	[1]			12,999,840
Reliance Bancshares, Inc.
Stock issued for acquisition, shares (in shares)		3,999,623
Landrum Company
Stock issued for acquisition, shares (in shares)		17,349,722

[1] All share and per share amounts for the year ended 2017 have been restated to reflect the effect of the two-for-one stock split on February 8, 2018.