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]	Treasury Stock [Member]
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2018		17,302,000
Shareholders' Equity, Beginning Balance at Dec. 31, 2018	$ 448,184	$ 1,081	$ 119,888	$ 355,524	$ (28,309)	$ 0
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			0
Common Stock, Shares Outstanding, Ending Balance at Mar. 31, 2019		17,305,000
Shareholders' Equity, Ending Balance at Mar. 31, 2019	469,843	$ 1,082	120,743	365,521	(17,503)	0
Cumulative effect of change in accounting principle	$ 722			722
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2019	17,363,455	17,363,000
Shareholders' Equity, Beginning Balance at Dec. 31, 2019	$ 503,492	$ 1,085	123,281	390,363	(11,237)	0
Net income	11,901			11,901
Total other comprehensive income (loss), net of tax	12,166				12,166
Cash dividends declared	(8,913)			(8,913)
Share-based compensation	758		758
Exercise of stock options and issuance of other compensation-related equity awards, shares		14,000
Exercise of stock options and issuance of other compensation-related equity awards, value	$ (377)	$ 0	(872)			495
Common Stock, Shares Outstanding, Ending Balance at Mar. 31, 2020	17,251,532	17,252,000
Shareholders' Equity, Ending Balance at Mar. 31, 2020	$ 508,597	$ 1,085	$ 123,167	387,243	$ 929	(3,827)
Treasury stock, shares acquired	(124,863)
Treasury stock, amount acquired	$ (4,322)					$ (4,322)
Cumulative effect of change in accounting principle	$ (6,108)			$ (6,108)