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 (Loss), Net of Tax	Treasury Stock
Beginning balance (in shares) at Dec. 31, 2018			49,014,925					(1,514,984)
Beginning balance at Dec. 31, 2018	$ 1,456,347	$ (276)	$ 49,015	$ 1,051,584	$ 377,135	$ (276)	$ (4,826)	$ (16,561)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for acquisition (in shares)			22,181,522
Issuance of common stock for acquisition	869,294		$ 22,182	847,112
Issuance of restricted shares (in shares)			147,574
Issuance of restricted shares	915		$ 147	768
Forfeitures of restricted shares (in shares)			(40,423)
Forfeitures of restricted shares	(524)		$ (40)	(484)
Proceeds from exercise of stock options (in shares)			127,983
Proceeds from exercise of stock options	3,587		$ 143	3,444
Share-based compensation	2,365			2,365
Purchase of treasury shares (in shares)								322,764
Purchase of treasury shares	(11,561)							$ (11,561)
Net income (loss)	100,193				100,193
Dividends on common shares	(19,925)				(19,925)
Other comprehensive income (loss) during the period	20,308						20,308
Ending balance (in shares) at Sep. 30, 2019			71,431,581					(1,837,748)
Ending balance at Sep. 30, 2019	$ 2,420,723		$ 71,447	1,904,789	457,127		15,482	$ (28,122)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Beginning balance (in shares) at Dec. 31, 2018			49,014,925					(1,514,984)
Beginning balance at Dec. 31, 2018	$ 1,456,347	(276)	$ 49,015	1,051,584	377,135	(276)	(4,826)	$ (16,561)
Ending balance (in shares) at Dec. 31, 2019			71,499,829					(1,995,996)
Ending balance at Dec. 31, 2019	2,469,582	(56,704)	$ 71,500	1,907,108	507,950	(56,704)	17,995	$ (34,971)
Beginning balance (in shares) at Jun. 30, 2019			49,099,332					(1,837,748)
Beginning balance at Jun. 30, 2019	1,537,121		$ 49,099	1,053,500	446,182		16,462	$ (28,122)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for acquisition (in shares)			22,181,522
Issuance of common stock for acquisition	869,294		$ 22,182	847,112
Issuance of restricted shares (in shares)			30,452
Issuance of restricted shares	0		$ 30	(30)
Proceeds from exercise of stock options (in shares)			120,275
Proceeds from exercise of stock options	3,534		$ 136	3,398
Share-based compensation	809			809
Net income (loss)	21,384				21,384
Dividends on common shares	(10,439)				(10,439)
Other comprehensive income (loss) during the period	(980)						(980)
Ending balance (in shares) at Sep. 30, 2019			71,431,581					(1,837,748)
Ending balance at Sep. 30, 2019	$ 2,420,723		$ 71,447	1,904,789	457,127		15,482	$ (28,122)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Beginning balance (in shares) at Dec. 31, 2019			71,499,829					(1,995,996)
Beginning balance 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)			164,476
Issuance of restricted shares	289		$ 164	125
Forfeitures of restricted shares (in shares)			(11,250)
Forfeitures of restricted shares	(170)		$ (11)	(159)
Proceeds from exercise of stock options (in shares)			49,532
Proceeds from exercise of stock options	981		$ 50	931
Share-based compensation	3,026			3,026
Purchase of treasury shares (in shares)								216,045
Purchase of treasury shares	(7,989)							$ (7,989)
Net income (loss)	167,703				167,703
Dividends on common shares	(31,292)				(31,292)
Other comprehensive income (loss) during the period	19,257						19,257
Ending balance (in shares) at Sep. 30, 2020			71,702,587					(2,212,041)
Ending balance at Sep. 30, 2020	2,564,683		$ 71,703	1,911,031	587,657		37,252	$ (42,960)
Beginning balance (in shares) at Jun. 30, 2020			71,674,087					(2,211,305)
Beginning balance at Jun. 30, 2020	2,460,130		$ 71,674	1,909,839	481,948		39,613	$ (42,944)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted shares (in shares)			12,500
Issuance of restricted shares	0		$ 13	(13)
Proceeds from exercise of stock options (in shares)			16,000
Proceeds from exercise of stock options	280		$ 16	264
Share-based compensation	941			941
Purchase of treasury shares (in shares)								736
Purchase of treasury shares	(16)							$ (16)
Net income (loss)	116,145				116,145
Dividends on common shares	(10,436)				(10,436)
Other comprehensive income (loss) during the period	(2,361)						(2,361)
Ending balance (in shares) at Sep. 30, 2020			71,702,587					(2,212,041)
Ending balance at Sep. 30, 2020	$ 2,564,683		$ 71,703	$ 1,911,031	$ 587,657		$ 37,252	$ (42,960)