Note 2 - Acquisitions - Pro Forma Combined Operating Results (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Guaranty Bank and Trust Company [Member]
Net interest income	$ 122,923	$ 102,902
Noninterest income	32,703	34,238
Net income	$ 38,728	$ 27,103
Basic (in dollars per share)	$ 2.80	$ 2.05
Diluted (in dollars per share)	$ 2.73	$ 2.02
Community State Bank [Member]
Net interest income		$ 110,035	$ 98,483
Noninterest income		34,773	31,051
Net income		$ 34,137	$ 22,118
Basic (in dollars per share)		$ 2.62	$ 1.91
Diluted (in dollars per share)		$ 2.58	$ 1.89