Consolidated Statements of Shareholders' Equity $ in Thousands	USD ($)	Common Stock USD ($)	Treasury Stock USD ($)	Additional paid in capital USD ($)	Retained earnings USD ($)	Accumulated other comprehensive income (loss) USD ($)
Balance at Dec. 31, 2014	$ 316,241	$ 199	$ (1,743)	$ 207,731	$ 108,373	$ 1,681
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,450	0	0	0	38,450	0
Other comprehensive income (loss)	(1,463)	0	0	0	0	(1,463)
Cash dividends paid on common shares	(5,259)	0	0	0	(5,259)	0
Issuance under equity compensation plans, net	(1,190)	2	0	(1,192)	0	0
Share-based compensation	3,601	0	0	3,601	0	0
Excess tax benefit related to equity compensation plans	449	0	0	449	0	0
Balance at Dec. 31, 2015	$ 350,829	201	(1,743)	210,589	141,564	218
Total shares awarded to JCB shareholders	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 48,837	0	0	0	48,837	0
Other comprehensive income (loss)	(1,959)	0	0	0	0	(1,959)
Cash dividends paid on common shares	(8,211)	0	0	0	8,211	0
Repurchase of preferred stock	(4,889)	0	(4,889)	0	0	0
Issuance under equity compensation plans, net	(2,203)	2	0	(2,205)	0	0
Share-based compensation	3,367	0	0	3,367	0	0
Excess tax benefit related to equity compensation plans	1,327	0	0	1,327	0	0
Balance at Dec. 31, 2016	$ 387,098	203	(6,632)	213,078	182,190	(1,741)
Total shares awarded to JCB shareholders	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 48,190	0	0	0		0
Other comprehensive income (loss)	(2,077)	0	0	0	0	(2,077)
Cash dividends paid on common shares	(10,249)	0	0	0	(10,249)	0
Repurchase of preferred stock	(16,636)	0	(16,636)	0	0	0
Issuance under equity compensation plans, net	(2,909)	2	0	(2,911)	0	0
Shares issued in connection with acquisition of Jefferson County Bancshares, Inc., 3,299,865 shares, net	141,729	33	0	141,696	0	0
Share-based compensation	3,427	0	0	3,427	0	0
Reclassification for the adoption of ASU 2016-09	0	0	0	(5,229)	5,229	0
Balance at Dec. 31, 2017	$ 548,573	$ 238	$ (23,268)	$ 350,061	$ 225,360	$ (3,818)