Consolidated Statements of Shareholders’ Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Income, Net of Tax	Treasury Stock
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	$ (12,388)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)		2,549,469
Issuance of common stock		$ 2,549	69,906
Issuance of restricted shares (in shares)		125,581
Issuance of restricted shares		$ 126	(126)
Cancellation of restricted shares (in shares)		(7,085)
Cancellation of restricted shares		$ (7)	7
Exercise of stock options (in shares)		54,510
Proceeds from exercise of stock options		$ 55	908
Share-based compensation			1,586
Net income	$ 53,923			53,923
Dividends on common shares				(6,974)
Other comprehensive income during the period	7,096				7,096
Purchase of treasury shares (in shares)						42,556
Purchase of treasury shares						$ (1,225)
Balance at end of period (in shares) at Sep. 30, 2016		36,347,637				1,456,333
Balance at end of period at Sep. 30, 2016	642,583	$ 36,348	409,630	199,769	10,449	$ (13,613)
Balance at beginning of period (in shares) at Dec. 31, 2016		36,377,807				1,456,333
Balance at beginning of period at Dec. 31, 2016	646,437	$ 36,378	410,276	214,454	(1,058)	$ (13,613)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)		2,141,072
Issuance of common stock		$ 2,141	92,359
Issuance of restricted shares (in shares)		84,147
Issuance of restricted shares		$ 84	(84)
Cancellation of restricted shares (in shares)		(472)
Cancellation of restricted shares		$ 0	0
Exercise of stock options (in shares)		103,356
Proceeds from exercise of stock options		$ 103	1,809
Share-based compensation			2,419
Net income	64,398			64,398
Dividends on common shares				(11,158)
Other comprehensive income during the period	4,299				4,299
Purchase of treasury shares (in shares)						18,528
Purchase of treasury shares						$ (886)
Balance at end of period (in shares) at Sep. 30, 2017		38,705,910				1,474,861
Balance at end of period at Sep. 30, 2017	$ 801,921	$ 38,706	$ 506,779	$ 267,694	$ 3,241	$ (14,499)