Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($)	Total	Cumulative Change in Accounting Principal, Adjustment	Cumulative Change in Accounting Principal, Adjusted Balance	Common Stock	Common Stock Cumulative Change in Accounting Principal, Adjusted Balance	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Change in Accounting Principal, Adjusted Balance	Retained Earnings	Retained Earnings Cumulative Change in Accounting Principal, Adjustment	Retained Earnings Cumulative Change in Accounting Principal, Adjusted Balance	Deferred Compensation	Deferred Compensation Cumulative Change in Accounting Principal, Adjusted Balance	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Cumulative Change in Accounting Principal, Adjusted Balance	Treasury Stock	Treasury Stock Cumulative Change in Accounting Principal, Adjusted Balance
Beginning balance at Dec. 31, 2018	$ 475,864,000			$ 70,876,000		$ 293,937,000		$ 131,392,000			$ 2,761,000		$ (6,473,000)		$ (16,629,000)
Net income	35,967,000							35,967,000
Other comprehensive income, net of tax	15,895,000												15,895,000
Cash dividends on common stock	(6,000,000)							(6,000,000)
Issuance of common shares pursuant to the Dividend Reinvestment Plan	473,000			54,000		419,000
Issuance of common shares pursuant to the Deferred Compensation Plan	323,000			39,000		284,000
Issuance of restricted shares pursuant to the 2017 Stock Incentive Plan	864,000			104,000		760,000
Issuance of common shares pursuant to the Employee Stock Purchase Plan	149,000			19,000		130,000
Purchase of shares of treasury stock	(1,129,000)														(1,129,000)
Deferred Compensation											196,000				(196,000)
Tax benefit related to deferred compensation distributions	56,000					56,000
Grant of restricted units pursuant to 2017 Stock Incentive Plan	(866,000)					(52,000)					(814,000)
Vested restricted shares/units compensation expense	363,000										363,000
Ending balance at Sep. 30, 2019	521,959,000			71,092,000		295,534,000		161,359,000			2,506,000		9,422,000		(17,954,000)
Beginning balance at Jun. 30, 2019	508,958,000			71,075,000		295,415,000		149,688,000			2,323,000		7,216,000		(16,759,000)
Net income	11,670,000							11,670,000
Other comprehensive income, net of tax	2,206,000												2,206,000
Cash dividends on common stock	1,000							1,000
Issuance of common shares pursuant to the Deferred Compensation Plan	75,000			9,000		66,000
Issuance of common shares pursuant to the Employee Stock Purchase Plan	61,000			8,000		53,000
Purchase of shares of treasury stock	(1,129,000)														(1,129,000)
Deferred Compensation											66,000				(66,000)
Vested restricted shares/units compensation expense	117,000										117,000
Ending balance at Sep. 30, 2019	521,959,000			71,092,000		295,534,000		161,359,000			2,506,000		9,422,000		(17,954,000)
Beginning balance at Dec. 31, 2019	526,609,000		$ 525,892,000	71,152,000	$ 71,152,000	295,925,000	$ 295,925,000	166,667,000		$ 165,950,000	2,760,000	$ 2,760,000	8,360,000	$ 8,360,000	(18,255,000)	$ (18,255,000)
Beginning balance (ASU 2016-13) at Dec. 31, 2019		$ (717,000)							$ (717,000)
Net income	31,701,000							31,701,000
Other comprehensive income, net of tax	8,634,000												8,634,000
Cash dividends on common stock	(6,651,000)							(6,651,000)
Issuance of common shares pursuant to the Dividend Reinvestment Plan	336,000			54,000		282,000
Issuance of common shares pursuant to the Deferred Compensation Plan	228,000			33,000		195,000
Issuance of restricted shares pursuant to the 2017 Stock Incentive Plan	868,000			101,000		767,000
Issuance of common shares pursuant to the Employee Stock Purchase Plan	245,000			44,000		201,000
Deferred Compensation											208,000				(208,000)
Tax benefit related to deferred compensation distributions	22,000					22,000
Grant of restricted units pursuant to 2017 Stock Incentive Plan	584,000					584,000
Release of restricted units pursuant to 2017 Stock Incentive Plan	(516,000)					(516,000)
Vested restricted shares/units compensation expense	(334,000)										(334,000)
Ending balance at Sep. 30, 2020	561,009,000			71,384,000		297,460,000		191,000,000			2,634,000		16,994,000		(18,463,000)
Beginning balance at Jun. 30, 2020	549,273,000			71,370,000		297,392,000		179,435,000			2,364,000		17,105,000		(18,393,000)
Net income	11,565,000							11,565,000
Other comprehensive income, net of tax	(111,000)												(111,000)
Issuance of common shares pursuant to the Employee Stock Purchase Plan	82,000			14,000		68,000
Deferred Compensation											70,000				(70,000)
Vested restricted shares/units compensation expense	200,000										200,000
Ending balance at Sep. 30, 2020	$ 561,009,000			$ 71,384,000		$ 297,460,000		$ 191,000,000			$ 2,634,000		$ 16,994,000		$ (18,463,000)