CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2016	$ 426,978	$ 104,405	$ 327,873	$ (2,387)	$ (2,913)
Balance (in shares) at Dec. 31, 2016		24,937,865
Net income	14,514		14,514
Other comprehensive income (loss), net of tax	485			485
Cash dividends declared, $0.19 per share	(4,771)		(4,771)
Treasury shares purchased under deferred directors' plan	0	$ 220			(220)
Treasury shares purchased under deferred directors' plan (in shares)		(4,846)
Stock activity under equity compensation plans	(1,652)	$ (1,652)
Stock activity under equity compensation plans (in shares)		84,672
Stock based compensation expense	1,559	$ 1,559
Balance at Mar. 31, 2017	437,113	$ 104,532	337,616	(1,902)	(3,133)
Balance (in shares) at Mar. 31, 2017		25,017,691
Balance at Dec. 31, 2017	468,578	$ 108,862	363,794	(670)	(3,408)
Balance (in shares) at Dec. 31, 2017		25,025,933
Adoption of ASU | Accounting Standards Update 2018-02 [Member]	0		173	(173)
Adoption of ASU | Accounting Standards Update 2014-09 [Member]	24		24
Adoption of ASU | Accounting Standards Update 2016-01 [Member]	0		68	(68)
Net income	18,336		18,336
Other comprehensive income (loss), net of tax	(7,077)			(7,077)
Cash dividends declared, $0.19 per share	(5,545)		(5,545)
Treasury shares sold and distributed under deferred directors' plan	0	$ 185			(185)
Treasury shares sold and distributed under deferred directors' plan (in shares)		(3,807)
Treasury shares purchased under deferred directors' plan	0	$ (115)			115
Treasury shares purchased under deferred directors' plan (in shares)		5,636
Stock activity under equity compensation plans	(2,483)	$ (2,483)
Stock activity under equity compensation plans (in shares)		96,679
Stock based compensation expense	1,411	$ 1,411
Balance at Mar. 31, 2018	$ 473,244	$ 107,860	$ 376,850	$ (7,988)	$ (3,478)
Balance (in shares) at Mar. 31, 2018		25,124,441