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, 2015	$ 392,812	$ 99,123	$ 294,002	$ 2,142	$ (2,455)
Balance (in shares) at Dec. 31, 2015		24,819,066
Comprehensive income:
Net income	38,562		38,562
Other comprehensive income, net of tax	5,850			5,850
Cash dividends declared	(13,446)		(13,446)
Treasury shares purchased under deferred directors' plan	0	$ 428			(428)
Treasury shares purchased under deferred directors' plan (in shares)		(13,982)
Stock activity under equity compensation plans	319	$ 319
Stock activity under equity compensation plans (in shares)		118,646
Stock based compensation expense	3,194	$ 3,194
Fractional shares retired due to 3-for-2 stock split (in shares)		(36)
Balance at Sep. 30, 2016	427,291	$ 103,064	319,118	7,992	(2,883)
Balance (in shares) at Sep. 30, 2016		24,923,694
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
Comprehensive income:
Net income	45,703		45,703
Other comprehensive income, net of tax	2,839			2,839
Cash dividends declared	(15,866)		(15,866)
Treasury shares purchased under deferred directors' plan	0	$ 458			(458)
Treasury shares purchased under deferred directors' plan (in shares)		(9,992)
Stock activity under equity compensation plans	(1,736)	$ (1,736)
Stock activity under equity compensation plans (in shares)		98,816
Stock based compensation expense	4,509	$ 4,509
Balance at Sep. 30, 2017	$ 462,427	$ 107,636	$ 357,710	$ 452	$ (3,371)
Balance (in shares) at Sep. 30, 2017		25,026,689