Consolidated Statements of Shareholders’ Equity (unaudited) - USD ($) $ in Thousands	Total	Cumulative effect of change in accounting for credit losses	Common Stock	Capital Surplus	Retained Earnings	Retained Earnings Cumulative effect of change in accounting for credit losses	Accumulated Other Comprehensive Income, Net of Tax	Treasury Stock
Balance at beginning of period (in shares) at Dec. 31, 2019			71,499,829					1,995,996
Balance at beginning of period at Dec. 31, 2019	$ 2,469,582	$ (56,704)	$ 71,500	$ 1,907,108	$ 507,950	$ (56,704)	$ 17,995	$ (34,971)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted shares (in shares)			151,976
Issuance of restricted shares	289		$ 152	137
Forfeitures of restricted shares (in shares)			(11,250)
Forfeitures of restricted shares	(170)		$ (11)	(159)
Proceeds from exercise of stock options (in shares)			33,532
Proceeds from exercise of stock options	701		$ 33	668
Share-based compensation	2,085			2,085
Purchase of treasury shares (in shares)								215,309
Purchase of treasury shares	(7,973)							$ (7,973)
Net income	51,558				51,558
Dividends on common stock shares	(20,856)				(20,856)
Other comprehensive income (loss) during the period	21,618						21,618
Balance at end of period (in shares) at Jun. 30, 2020			71,674,087					2,211,305
Balance at end of period at Jun. 30, 2020	2,460,130		$ 71,674	1,909,839	481,948		39,613	$ (42,944)
Balance at beginning of period (in shares) at Mar. 31, 2020			71,651,986					2,210,712
Balance at beginning of period at Mar. 31, 2020	2,437,150		$ 71,652	1,908,721	460,153		39,551	$ (42,927)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted shares (in shares)			33,351
Issuance of restricted shares	0		$ 33	(33)
Forfeitures of restricted shares (in shares)			(11,250)
Forfeitures of restricted shares	(170)		$ (11)	(159)
Share-based compensation	1,310			1,310
Purchase of treasury shares (in shares)								593
Purchase of treasury shares	(17)							$ (17)
Net income	32,236				32,236
Dividends on common stock shares	(10,441)				(10,441)
Other comprehensive income (loss) during the period	62						62
Balance at end of period (in shares) at Jun. 30, 2020			71,674,087					2,211,305
Balance at end of period at Jun. 30, 2020	2,460,130		$ 71,674	1,909,839	481,948		39,613	$ (42,944)
Balance at beginning of period (in shares) at Dec. 31, 2020			71,753,705					2,212,224
Balance at beginning of period at Dec. 31, 2020	2,647,088		$ 71,754	1,913,285	671,510		33,505	$ (42,966)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted shares (in shares)			99,308
Issuance of restricted shares	599		$ 99	500
Forfeitures of restricted shares (in shares)			(750)
Forfeitures of restricted shares	(20)		$ (1)	(19)
Proceeds from exercise of stock options (in shares)			155,608
Proceeds from exercise of stock options	4,211		$ 156	4,055
Share-based compensation	2,745			2,745
Purchase of treasury shares (in shares)								28,438
Purchase of treasury shares	(1,456)							$ (1,456)
Net income	213,289				213,289
Dividends on common stock shares	(20,971)				(20,971)
Other comprehensive income (loss) during the period	(8,481)						(8,481)
Balance at end of period (in shares) at Jun. 30, 2021			72,007,871					2,240,662
Balance at end of period at Jun. 30, 2021	2,837,004		$ 72,008	1,920,566	863,828		25,024	$ (44,422)
Balance at beginning of period (in shares) at Mar. 31, 2021			71,954,088					2,240,662
Balance at beginning of period at Mar. 31, 2021	2,757,596		$ 71,954	1,917,990	785,984		26,090	$ (44,422)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted shares (in shares)			13,233
Issuance of restricted shares	0		$ 13	(13)
Forfeitures of restricted shares (in shares)			(750)
Forfeitures of restricted shares	(20)		$ (1)	(19)
Proceeds from exercise of stock options (in shares)			41,300
Proceeds from exercise of stock options	1,209		$ 42	1,167
Share-based compensation	1,441			1,441
Purchase of treasury shares	0
Net income	88,327				88,327
Dividends on common stock shares	(10,483)				(10,483)
Other comprehensive income (loss) during the period	(1,066)						(1,066)
Balance at end of period (in shares) at Jun. 30, 2021			72,007,871					2,240,662
Balance at end of period at Jun. 30, 2021	$ 2,837,004		$ 72,008	$ 1,920,566	$ 863,828		$ 25,024	$ (44,422)