Condensed Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]		Accumulated Other Comprehensive (Loss) Income [Member]		Treasury Stock [Member]
Beginning balance at Dec. 31, 2016	$ 505,209	$ 144,559	$ 230,494	$ 194,516		$ (19,454)		$ (44,906)
Beginning balance, shares at Dec. 31, 2016		26,589,353
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	22,634	$ 0	0	22,634		0		0
Other comprehensive loss, net of income tax benefit	2,272	0	0	0		2,272		0
Cash dividends declared ($0.40 per share)	(10,652)	0	0	(10,652)		0		0
Stock issued under dividend reinvestment and employee stock purchase plans	1,229	$ 0	72	0		0		1,157
Stock issued under dividend reinvestment and employee stock purchase plans, shares		43,415
Exercise of stock options	1,328	$ 0	(105)	0		0		1,433
Exercise of stock options, shares		73,870
Stock-based compensation	1,708	$ 0	1,708	0		0		0
Purchases of treasury stock	(2,422)	$ 0	0	0		0		(2,422)
Purchases of treasury stock, shares		(83,970)
Restricted stock awards granted, net of cancellations	0	$ 0	(880)	0		0		880
Restricted stock awards granted, net of cancellations, shares		45,323
Ending balance at Jun. 30, 2017	521,306	$ 144,559	231,289	206,498		(17,182)		(43,858)
Ending balance, shares at Jun. 30, 2017		26,667,991
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Pronouncement in Period of Adoption | Accounting Standards Update 2016-01 [Member]	0	$ 0	0	433	[1]	(433)	[1],[2]	0
Cumulative Effect of New Accounting Pronouncement in Period of Adoption | Accounting Standards Update 2018-02 [Member]	0	0	0	3,921	[1]	(3,921)	[1],[2]	0
Beginning balance at Dec. 31, 2017	603,374	$ 157,784	290,133	216,761		(17,771)		(43,533)
Beginning balance, shares at Dec. 31, 2017		29,334,859
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17,207	$ 0	0	17,207		0		0
Other comprehensive loss, net of income tax benefit	(5,882)	0	0	0		(5,882)		0
Cash dividends declared ($0.40 per share)	(11,749)	0	0	(11,749)		0		0
Stock issued under dividend reinvestment and employee stock purchase plans	1,173	$ 0	98	1		0		1,074
Stock issued under dividend reinvestment and employee stock purchase plans, shares		41,939
Exercise of stock options	$ 711	$ 0	(14)	0		0		725
Exercise of stock options, shares	36,990	36,990
Stock-based compensation	$ 1,719	$ 0	1,719	0		0		0
Purchases of treasury stock	(1,259)	$ 0	0	0		0		(1,259)
Purchases of treasury stock, shares		(44,353)
Restricted stock awards granted, net of cancellations	0	$ 0	(698)	0		0		698
Restricted stock awards granted, net of cancellations, shares		37,015
Ending balance at Jun. 30, 2018	$ 605,294	$ 157,784	$ 291,238	$ 226,574		$ (28,007)		$ (42,295)
Ending balance, shares at Jun. 30, 2018		29,406,450

[1] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2018" for additional information.

[2] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2018" for additional information.