Consolidated Statements of Stockholders' Equity (Parentheticals)		12 Months Ended
		Dec. 31, 2018 $ / shares shares	Dec. 31, 2017 $ / shares shares		Dec. 31, 2016 $ / shares shares
Stock issued for employee stock purchase plan, shares (in shares)		39,782	26,002	[1]	31,470	[1]
Stock issued for compensation plans, shares (in shares)		278,743	359,286	[1]	295,630	[1]
Cash dividends, per share (in dollars per share) | $ / shares		$ 0.60	$ 0.50	[1]	$ 0.48	[1]
Citizens National Bank
Stock issued for acquisition, shares (in shares)	[1]				1,671,482
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

[1] All share and per share amounts for the years ended 2017 and 2016 have been restated to reflect the effect of the two-for-one stock split on February 8, 2018.