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]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-01	$ 0		$ 0	$ 0	$ 433		$ (433)		$ 0
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2018-02	0		0	0	3,921		(3,921)		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 income, net of income tax	(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
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
Beginning balance at Mar. 31, 2018	606,719		$ 157,784	290,095	228,097		(26,791)		(42,466)
Beginning balance, shares at Mar. 31, 2018			29,391,934
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,357		$ 0	0	4,357		0		0
Other comprehensive income, net of income tax	(1,216)		0	0	0		(1,216)		0
Cash dividends declared ($0.40 per share)	(5,881)		0	0	(5,881)		0		0
Stock issued under dividend reinvestment and employee stock purchase plans	604		$ 0	54	1		0		549
Stock issued under dividend reinvestment and employee stock purchase plans, shares			21,686
Exercise of stock options	443		$ 0	(5)	0		0		448
Exercise of stock options, shares			22,832
Stock-based compensation	872		$ 0	872	0		0		0
Purchases of treasury stock	(604)		$ 0	0	0		0		(604)
Purchases of treasury stock, shares			(20,814)
Restricted stock awards granted, net of cancellations	0		$ 0	222	0		0		(222)
Restricted stock awards granted, net of cancellations, shares			(9,188)
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-02	(1,525)	[1]	$ 0	0	(1,525)	[1]	0		0
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2017-12	0		0	0	(83)	[1]	83	[1],[2]	0
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2017-08	(39)	[1]	0	0	(39)	[1]	0		0
Beginning balance at Dec. 31, 2018	624,133		$ 157,784	292,401	248,167		(28,416)		(45,803)
Beginning balance, shares at Dec. 31, 2018			29,270,852
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32,547		$ 0	0	32,547		0		0
Other comprehensive income, net of income tax	6,384		0	0	0		6,384		0
Cash dividends declared ($0.40 per share)	(11,711)		0	0	(11,711)		0		0
Stock issued under dividend reinvestment and employee stock purchase plans	1,135		$ 0	77	1		0		1,057
Stock issued under dividend reinvestment and employee stock purchase plans, shares			48,183
Exercise of stock options	$ 691		$ 0	(102)	0		0		793
Exercise of stock options, shares	39,500		39,500
Stock-based compensation	$ 1,230		$ 0	1,230	0		0		0
Purchases of treasury stock	(1,175)		$ 0	0	0		0		(1,175)
Purchases of treasury stock, shares			(46,244)
Cancellations of performance-based restricted stock awards	0		$ 0	341	0		0		(341)
Cancellations of performance-based restricted stock awards, shares			(17,349)
Ending balance at Jun. 30, 2019	651,670		$ 157,784	293,947	267,357		(21,949)		(45,469)
Ending balance, shares at Jun. 30, 2019			29,294,942
Beginning balance at Mar. 31, 2019	637,606		$ 157,784	293,255	256,746		(24,238)		(45,941)
Beginning balance, shares at Mar. 31, 2019			29,272,502
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,468		$ 0	0	16,468		0		0
Other comprehensive income, net of income tax	2,289		0	0	0		2,289		0
Cash dividends declared ($0.40 per share)	(5,858)		0	0	(5,858)		0		0
Stock issued under dividend reinvestment and employee stock purchase plans	564		$ 0	47	1		0		516
Stock issued under dividend reinvestment and employee stock purchase plans, shares			22,440
Exercise of stock options	170		$ 0	(11)	0		0		181
Exercise of stock options, shares			9,000
Stock-based compensation	656		$ 0	656	0		0		0
Purchases of treasury stock	(225)		$ 0	0	0		0		(225)
Purchases of treasury stock, shares			(9,000)
Ending balance at Jun. 30, 2019	$ 651,670		$ 157,784	$ 293,947	$ 267,357		$ (21,949)		$ (45,469)
Ending balance, shares at Jun. 30, 2019			29,294,942

[1] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2019" for additional information.

[2] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2019" for additional information.