CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2017		17,227,000
Shareholders' Equity, Beginning Balance at Dec. 31, 2017	$ 413,284	$ 1,077	$ 117,961	$ 317,756	$ (23,510)
Net income	16,211			16,211
Total other comprehensive income (loss), net of tax	(9,165)				(9,165)
Cash dividends declared	(7,462)			(7,462)
Share-based compensation	669		669
Exercise of stock options and issuance of other compensation-related equity awards, shares		35,000
Exercise of stock options and issuance of other compensation-related equity awards, value	(456)	$ 2	(458)
Common Stock, Shares Outstanding, Ending Balance at Mar. 31, 2018		17,262,000
Shareholders' Equity, Ending Balance at Mar. 31, 2018	$ 413,081	$ 1,079	118,172	326,505	(32,675)
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2018	17,302,037	17,302,000
Shareholders' Equity, Beginning Balance at Dec. 31, 2018	$ 448,184	$ 1,081	119,888	355,524	(28,309)
Net income	17,495			17,495
Total other comprehensive income (loss), net of tax	10,806				10,806
Cash dividends declared	(8,220)			(8,220)
Share-based compensation	740		740
Exercise of stock options and issuance of other compensation-related equity awards, shares		3,000
Exercise of stock options and issuance of other compensation-related equity awards, value	$ 116	$ 1	115
Common Stock, Shares Outstanding, Ending Balance at Mar. 31, 2019	17,305,279	17,305,000
Shareholders' Equity, Ending Balance at Mar. 31, 2019	$ 469,843	$ 1,082	$ 120,743	365,521	$ (17,503)
Cumulative effect of change in accounting principle	$ 722			$ 722