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, 2016		17,171,000
Stockholders' equity, beginning 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		17,227,000
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)
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
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)
Cumulative effect of change in accounting principle	$ 722			$ 722