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	33,885			33,885
Total other comprehensive income (loss), net of tax	(11,552)				(11,552)
Cash dividends declared	(14,971)			(14,971)
Share-based compensation	1,319		1,319
Exercise of stock options and issuance of other compensation-related equity awards, shares		51,000
Exercise of stock options and issuance of other compensation-related equity awards, value	(394)	$ 3	(397)
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2018		17,278,000
Shareholders' Equity, Ending Balance at Jun. 30, 2018	421,571	$ 1,080	118,883	336,670	(35,062)
Common Stock, Shares Outstanding, Beginning Balance at Mar. 31, 2018		17,262,000
Shareholders' Equity, Beginning Balance at Mar. 31, 2018	413,081	$ 1,079	118,172	326,505	(32,675)
Net income	17,674			17,674
Total other comprehensive income (loss), net of tax	(2,387)				(2,387)
Cash dividends declared	(7,509)			(7,509)
Share-based compensation	649		649
Exercise of stock options and issuance of other compensation-related equity awards, shares		16,000
Exercise of stock options and issuance of other compensation-related equity awards, value	63	$ 1	62
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2018		17,278,000
Shareholders' Equity, Ending Balance at Jun. 30, 2018	$ 421,571	$ 1,080	118,883	336,670	(35,062)
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	34,768			34,768
Total other comprehensive income (loss), net of tax	16,443				16,443
Cash dividends declared	(17,141)			(17,141)
Share-based compensation	1,503		1,503
Exercise of stock options and issuance of other compensation-related equity awards, shares		34,000
Exercise of stock options and issuance of other compensation-related equity awards, value	$ (274)	$ 2	(276)
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2019	17,335,869	17,336,000
Shareholders' Equity, Ending Balance at Jun. 30, 2019	$ 484,205	$ 1,083	121,115	373,873	(11,866)
Common Stock, Shares Outstanding, Beginning Balance at Mar. 31, 2019		17,305,000
Shareholders' Equity, Beginning Balance at Mar. 31, 2019	469,843	$ 1,082	120,743	365,521	(17,503)
Net income	17,273			17,273
Total other comprehensive income (loss), net of tax	5,637				5,637
Cash dividends declared	(8,921)			(8,921)
Share-based compensation	764		764
Exercise of stock options and issuance of other compensation-related equity awards, shares		31,000
Exercise of stock options and issuance of other compensation-related equity awards, value	$ (391)	$ 1	(392)
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2019	17,335,869	17,336,000
Shareholders' Equity, Ending Balance at Jun. 30, 2019	$ 484,205	$ 1,083	$ 121,115	$ 373,873	$ (11,866)