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)			118,625
Issuance of restricted shares	290		$ 119	171
Proceeds from exercise of stock options (in shares)			33,532
Proceeds from exercise of stock options	701		$ 33	668
Share-based compensation	774			774
Purchase of treasury shares (in shares)								214,716
Purchase of treasury shares	(7,956)							$ (7,956)
Net income	19,322				19,322
Dividends, Common Stock, Cash	(10,415)				(10,415)
Other comprehensive income (loss) during the period	21,556						21,556
Balance at end of period (in shares) at Mar. 31, 2020			71,651,986					(2,210,712)
Balance at end of period at Mar. 31, 2020	2,437,150		$ 71,652	1,908,721	460,153		39,551	$ (42,927)
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)			86,075
Issuance of restricted shares	599		$ 86	513
Proceeds from exercise of stock options (in shares)			114,308
Proceeds from exercise of stock options	3,002		$ 114	2,888
Share-based compensation	1,304			1,304
Purchase of treasury shares (in shares)								28,438
Purchase of treasury shares	(1,456)							$ (1,456)
Net income	124,962				124,962
Dividends, Common Stock, Cash	(10,488)				(10,488)
Other comprehensive income (loss) during the period	(7,415)						(7,415)
Balance at end of period (in shares) at Mar. 31, 2021			71,954,088					(2,240,662)
Balance at end of period at Mar. 31, 2021	$ 2,757,596		$ 71,954	$ 1,917,990	$ 785,984		$ 26,090	$ (44,422)