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, 2015	$ 236,674	$ 17,180	$ 94,544	$ 122,493	$ 2,457
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,591			40,591
Other comprehensive (loss) income, 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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Initial fair value election on mortgage servicing rights, net of taxes of $396	615			615
Net income	52,398			52,398
Other comprehensive (loss) income, net of taxes	1,674				1,674
Reclassification of the income tax effects of the Tax Cuts and Jobs Act to Retained earnings (Note 13)	0			652	(652)
Common stock issued, net of offering costs	152,721	4,807	147,914
Common stock issued in conjunction with acquisition of the Clayton Banks (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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	80,236			80,236
Other comprehensive (loss) income, net of taxes	(4,484)				(4,484)
Stock based compensation expense	7,207	17	7,190
Restricted stock units vested and distributed, net of shares withheld	(2,664)	143	(2,807)
Shares issued under employee stock purchase program	1,196	29	1,167
Cash dividends declared	(6,363)			(6,363)
Balance at Dec. 31, 2018	$ 671,857	$ 30,725	$ 424,146	$ 221,213	$ (4,227)