Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance at Dec. 31, 2019	$ 315	$ 226,691	$ (71,487)	$ 433,960	$ (9,807)	$ 579,672
Impact of adoption of ASC 326 - Credit Losses				(875)		(875)
Net income				(1,390)		(1,390)
Award of common shares released from Employee Benefit Trust		1,398				1,398
Vesting of restricted stock unit awards		(5,626)	5,782	(156)
Stock-based compensation expense		3,430				3,430
Purchase of treasury shares			(2,342)			(2,342)
Repurchase of shares to satisfy tax obligation			(1,493)			(1,493)
Dividends on common stock				(6,084)		(6,084)
Other comprehensive income (loss)					(22,633)	(22,633)
Balance at Mar. 31, 2020	315	225,893	(69,540)	425,455	(32,440)	549,683
Balance at Dec. 31, 2019	315	226,691	(71,487)	433,960	(9,807)	579,672
Net income						31,213
Other comprehensive income (loss)					(8,501)	(8,501)
Balance at Sep. 30, 2020	315	227,877	(69,409)	445,931	(18,308)	586,406
Balance at Mar. 31, 2020	315	225,893	(69,540)	425,455	(32,440)	549,683
Net income				18,272		18,272
Award of common shares released from Employee Benefit Trust		40				40
Vesting of restricted stock unit awards		(133)	134	(1)
Stock-based compensation expense		1,101				1,101
Repurchase of shares to satisfy tax obligation			(30)			(30)
Dividends on common stock				(6,063)		(6,063)
Other comprehensive income (loss)					8,918	8,918
Balance at Jun. 30, 2020	315	226,901	(69,436)	437,663	(23,522)	571,921
Net income				14,331		14,331
Award of common shares released from Employee Benefit Trust		31				31
Vesting of restricted stock unit awards		(34)	34
Stock-based compensation expense		979				979
Purchase of treasury shares			(7)			(7)
Dividends on common stock				(6,063)		(6,063)
Other comprehensive income (loss)					5,214	5,214
Balance at Sep. 30, 2020	315	227,877	(69,409)	445,931	(18,308)	586,406
Balance at Dec. 31, 2020	341	261,533	(69,400)	442,789	(16,266)	618,997
Net income				19,039		19,039
Award of common shares released from Employee Benefit Trust		74				74
Vesting of restricted stock unit awards		(5,058)	5,211	(153)
Stock-based compensation expense		3,470				3,470
Repurchase of shares to satisfy tax obligation			(1,290)			(1,290)
Dividends on common stock				(6,652)		(6,652)
Other comprehensive income (loss)					5,563	5,563
Balance at Mar. 31, 2021	341	260,019	(65,479)	455,023	(10,703)	639,201
Balance at Dec. 31, 2020	341	261,533	(69,400)	442,789	(16,266)	618,997
Net income						63,710
Other comprehensive income (loss)					7,332	7,332
Balance at Sep. 30, 2021	341	262,009	(71,738)	486,418	(8,934)	668,096
Balance at Mar. 31, 2021	341	260,019	(65,479)	455,023	(10,703)	639,201
Net income				19,258		19,258
Award of common shares released from Employee Benefit Trust		91				91
Vesting of restricted stock unit awards		(221)	229	(8)
Stock-based compensation expense		1,069				1,069
Repurchase of shares to satisfy tax obligation			(85)			(85)
Dividends on common stock				(6,653)		(6,653)
Other comprehensive income (loss)					2,286	2,286
Balance at Jun. 30, 2021	341	260,958	(65,335)	467,620	(8,417)	655,167
Net income				25,413		25,413
Award of common shares released from Employee Benefit Trust		74				74
Stock-based compensation expense		977				977
Purchase of treasury shares			(6,403)			(6,403)
Dividends on common stock				(6,615)		(6,615)
Other comprehensive income (loss)					(517)	(517)
Balance at Sep. 30, 2021	$ 341	$ 262,009	$ (71,738)	$ 486,418	$ (8,934)	$ 668,096