CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Stockholders' Equity, Total
Equity Balance at Dec. 31, 2019	$ 143	$ 33,510	$ 537,167	$ 32,246		$ 603,066
Net income			41,525			41,525
Stock issued under Stock Option Plan		1,029			$ 133	1,162
Common dividends declared			(28,631)			(28,631)
Other comprehensive gain (loss)				23,388		23,388
Purchase of the Company's common stock					(15,867)	(15,867)
Reclassification of treasury stock per Maryland law	(4)		(15,730)		15,734
Equity Balance at Sep. 30, 2020	139	34,539	534,331	55,634		624,643
Equity Balance at Jun. 30, 2020	141	34,230	533,346	59,011		626,728
Net income			13,454			13,454
Stock issued under Stock Option Plan		309			37	346
Common dividends declared			(4,790)			(4,790)
Other comprehensive gain (loss)				(3,377)		(3,377)
Purchase of the Company's common stock					(7,718)	(7,718)
Reclassification of treasury stock per Maryland law	(2)		(7,679)		7,681
Equity Balance at Sep. 30, 2020	139	34,539	534,331	55,634		624,643
Equity Balance at Dec. 31, 2020	138	35,004	541,448	53,151		629,741
Net income			59,346			59,346
Stock issued under Stock Option Plan		2,464			1,074	3,538
Common dividends declared			(14,124)			(14,124)
Other comprehensive gain (loss)				(15,912)		(15,912)
Purchase of the Company's common stock					(23,773)	(23,773)
Reclassification of treasury stock per Maryland law	(4)		(22,695)		22,699
Equity Balance (CECL adoption) at Sep. 30, 2021			(14,175)			(14,175)
Equity Balance at Sep. 30, 2021	134	37,468	549,800	37,239		624,641
Equity Balance at Jun. 30, 2021	137	36,880	550,301	42,239		629,557
Net income			20,364			20,364
Stock issued under Stock Option Plan		588			257	845
Common dividends declared			(4,812)			(4,812)
Other comprehensive gain (loss)				(5,000)		(5,000)
Purchase of the Company's common stock					(16,313)	(16,313)
Reclassification of treasury stock per Maryland law	(3)		(16,053)		$ 16,056
Equity Balance (CECL adoption) at Sep. 30, 2021			(14,175)			(14,175)
Equity Balance at Sep. 30, 2021	$ 134	$ 37,468	$ 549,800	$ 37,239		$ 624,641