Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss), Net of Tax	Accumulated Other Comprehensive Income (Loss), Net of Tax Interest Rate Swap	Accumulated Other Comprehensive Income (Loss), Net of Tax Available-for-sale Securities	Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting for derivatives				$ 0
Adjusted balance, January 1, 2018				152,820		$ 152	$ 3,201
Balance at beginning of period (in shares) at Dec. 31, 2015		33,625,162						1,413,777
Balance at beginning of period at Dec. 31, 2015		$ 33,625	$ 337,349	152,820	$ 3,353	152	3,201	$ (12,388)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification to retained earnings due to change in federal corporate tax rate				0		0	0
Issuance of common stock (in shares)		2,549,469
Issuance of common stock		$ 2,549	69,906
Exercise of stock options (in shares)		54,510
Exercise of stock options		$ 55	909
Issuance of restricted shares (in shares)		155,751
Issuance of restricted shares		$ 156	(156)
Forfeitures of restricted shares (in shares)		(7,085)
Forfeitures of restricted shares		$ (7)	7
Share-based compensation			2,261
Net income	$ 72,100			72,100
Dividends on common shares				(10,466)
Change during period	(4,411)					24	(4,435)
Purchase of treasury shares (in shares)								42,556
Purchase of treasury shares								$ (1,225)
Balance at end of period (in shares) at Dec. 31, 2016		36,377,807						1,456,333
Balance at end of period at Dec. 31, 2016	646,437	$ 36,378	410,276	214,454	(1,058)	176	(1,234)	$ (13,613)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting for derivatives				0
Adjusted balance, January 1, 2018				214,454		176	(1,234)
Reclassification to retained earnings due to change in federal corporate tax rate				0		0	0
Issuance of common stock (in shares)		2,141,072
Issuance of common stock		$ 2,141	92,359
Exercise of stock options (in shares)		132,319
Exercise of stock options		$ 132	2,537
Issuance of restricted shares (in shares)		84,147
Issuance of restricted shares		$ 84	(84)
Forfeitures of restricted shares (in shares)		(472)
Forfeitures of restricted shares		$ 0	0
Share-based compensation			3,316
Net income	73,548			73,548
Dividends on common shares				(14,883)
Change during period	(222)					116	(338)
Purchase of treasury shares (in shares)								18,528
Purchase of treasury shares								$ (886)
Balance at end of period (in shares) at Dec. 31, 2017		38,734,873						1,474,861
Balance at end of period at Dec. 31, 2017	804,479	$ 38,735	508,404	273,119	(1,280)	292	(1,572)	$ (14,499)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting for derivatives				28
Adjusted balance, January 1, 2018	(1,672)			273,539		239	(1,911)
Reclassification to retained earnings due to change in federal corporate tax rate	(392)			392		(53)	(339)
Issuance of common stock (in shares)		10,124,491
Issuance of common stock		$ 10,124	537,003
Exercise of stock options (in shares)		76,286
Exercise of stock options		$ 76	838
Issuance of restricted shares (in shares)		89,855
Issuance of restricted shares		$ 90	(90)
Forfeitures of restricted shares (in shares)		(10,580)
Forfeitures of restricted shares		$ (10)	10
Share-based compensation			5,419
Net income	121,027			121,027
Dividends on common shares				(17,431)
Change during period	(3,154)					112	(3,266)
Purchase of treasury shares (in shares)								40,123
Purchase of treasury shares								$ (2,062)
Balance at end of period (in shares) at Dec. 31, 2018		49,014,925						1,514,984
Balance at end of period at Dec. 31, 2018	$ 1,456,347	$ 49,015	$ 1,051,584	$ 377,135	$ (4,826)	$ 351	$ (5,177)	$ (16,561)