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]	Treasury Stock [Member]
Common stock, shares outstanding, beginning balance at Dec. 31, 2017		17,227,000
Stockholders' equity, beginning balance at Dec. 31, 2017	$ 413,284	$ 1,077	$ 117,961	$ 317,756	$ (23,510)	$ 0
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)			0
Common stock, shares outstanding, ending balance at Dec. 31, 2018		17,302,000
Stockholders' equity, ending balance at Dec. 31, 2018	448,184	$ 1,081	119,888	355,524	(28,309)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	69,118			69,118
Total other comprehensive income (loss), net of tax	17,072				17,072
Cash dividends declared	(35,001)			(35,001)
Share-based compensation	3,124		3,124
Exercise of stock options, issuance of other compensation-related equity awards, net of awards surrendered, shares		61,000
Exercise of stock options, issuance of other compensation-related equity awards, net of awards surrendered	$ 273	$ 4	269			0
Common stock, shares outstanding, ending balance at Dec. 31, 2019	17,363,455	17,363,000
Stockholders' equity, ending balance at Dec. 31, 2019	$ 503,492	$ 1,085	123,281	390,363	(11,237)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	69,829			69,829
Total other comprehensive income (loss), net of tax	3,846				3,846
Cash dividends declared	(35,838)			(35,838)
Share-based compensation	3,766		3,766
Exercise of stock options, issuance of other compensation-related equity awards, net of awards surrendered, shares		27,000
Exercise of stock options, issuance of other compensation-related equity awards, net of awards surrendered	$ (470)	$ 0	(1,437)			967
Treasury stock purchased, shares	(125,000)
Treasury stock purchased	$ (4,322)					(4,322)
Common stock, shares outstanding, ending balance at Dec. 31, 2020	17,265,337	17,265,000
Stockholders' equity, ending balance at Dec. 31, 2020	$ 534,195	$ 1,085	$ 125,610	$ 418,246	$ (7,391)	$ (3,355)