CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - 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, 2015		17,020,000
Stockholders' equity, beginning balance at Dec. 31, 2015	$ 375,388	$ 1,064	$ 110,949	$ 273,074	$ (9,699)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	46,481			46,481
Total other comprehensive income (loss), net of tax	(10,058)				(10,058)
Cash dividends declared	(25,190)			(25,190)
Share-based compensation	2,190		2,190
Exercise of stock options, issuance of other compensation-related equity awards and related tax benefit, net of awards surrendered, shares		151,000
Exercise of stock options, issuance of other compensation related equity awards and related tax benefit, net of awards surrendered	1,993	$ 9	1,984
Common stock, shares outstanding, ending balance at Dec. 31, 2016		17,171,000
Stockholders' equity, ending balance at Dec. 31, 2016	390,804	$ 1,073	115,123	294,365	(19,757)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	45,925			45,925
Total other comprehensive income (loss), net of tax	472				472
Cash dividends declared	(26,759)			(26,759)
Share-based compensation	2,577		2,577
Exercise of stock options, issuance of other compensation-related equity awards, net of awards surrendered, shares		56,000
Exercise of stock options, issuance of other compensation-related equity awards, net of awards surrendered	265	$ 4	261
Reclassification of income tax effects due to the adoption of ASU 2018-02	$ 0			4,225	(4,225)
Common stock, shares outstanding, ending balance at Dec. 31, 2017	17,226,508	17,227,000
Stockholders' equity, ending balance at Dec. 31, 2017	$ 413,284	$ 1,077	117,961	317,756	(23,510)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	68,432			68,432
Total other comprehensive income (loss), net of tax	(4,799)				(4,799)
Cash dividends declared	(30,664)			(30,664)
Share-based compensation	2,602		2,602
Exercise of stock options, issuance of other compensation-related equity awards, net of awards surrendered, shares		75,000
Exercise of stock options, issuance of other compensation-related equity awards, net of awards surrendered	$ (671)	$ 4	(675)
Common stock, shares outstanding, ending balance at Dec. 31, 2018	17,302,037	17,302,000
Stockholders' equity, ending balance at Dec. 31, 2018	$ 448,184	$ 1,081	$ 119,888	$ 355,524	$ (28,309)