Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income, Net
Balance at Dec. 31, 2014	$ 215,228	$ 17,180	$ 94,544	$ 98,237	$ 5,267
Net income	47,856			47,856
Other comprehensive income (loss), net of taxes	(2,810)				(2,810)
Cash dividends declared	(23,600)			(23,600)
Balance at Dec. 31, 2015	236,674	17,180	94,544	122,493	2,457
Net income	40,591			40,591
Other comprehensive income (loss), net of taxes	(3,331)				(3,331)
Common stock issued, net of offering costs	115,525	6,765	108,760
Conversion of cash to stock-settled awards for, Equity based incentive plans	2,388		2,388
Conversion of cash to stock-settled awards for, Deferred compensation plan	3,000		3,000
Stock based compensation expense	4,693		4,693
Restricted stock units vested and distributed, net of shares withheld	(271)	142	(413)
Shares issued under employee stock purchase program	529	21	508
Cash dividends declared	(69,300)			(69,300)
Balance at Dec. 31, 2016	330,498	24,108	213,480	93,784	(874)
Initial fair value election on mortgage servicingrights, net of taxes of $396 (See Note 1)	615			615
Net income	52,398			52,398
Other comprehensive income (loss), net of taxes	1,674				1,674
Reclassification of the income tax effects of the TaxCuts and Jobs Act to Retained earnings (Note 15)				652	(652)
Common stock issued, net of offering costs	152,721	4,807	147,914
Common stock issued in conjunction withacquisition of the Clayton Banks, net ofissuance costs (See Note 2)	52,284	1,521	50,763
Stock based compensation expense	6,760	18	6,742
Restricted stock units vested and distributed, net of shares withheld	(856)	63	(919)
Shares issued under employee stock purchase program	635	19	616
Balance at Dec. 31, 2017	$ 596,729	$ 30,536	$ 418,596	$ 147,449	$ 148