Consolidated Statements of Shareholders’ Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Retained Earnings	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	$ 49,015	$ 1,051,584	$ 377,135	$ (4,826)	$ (16,561)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted shares (in shares)		117,122
Issuance of restricted shares	915	$ 116	799
Forfeitures of restricted shares (in shares)		(40,423)
Forfeitures of restricted shares	(524)	$ (40)	(484)
Proceeds from exercise of stock options (in shares)		7,708
Proceeds from exercise of stock options	54	$ 8	46
Share-based compensation	1,555		1,555
Purchase of treasury shares (in shares)						322,764
Purchase of treasury shares	(11,561)					$ (11,561)
Net income	78,809			78,809
Dividends on common shares	(9,486)			(9,486)
Other comprehensive income (loss) during the period	21,288				21,288
Ending balance (in shares) at Jun. 30, 2019		49,099,332				1,837,748
Ending balance at Jun. 30, 2019	1,537,121	$ 49,099	1,053,500	446,182	16,462	$ (28,122)
Beginning balance (in shares) at Mar. 31, 2019		49,126,427				1,541,118
Beginning balance at Mar. 31, 2019	1,495,584	$ 49,126	1,053,190	412,005	(1,178)	$ (17,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted shares (in shares)		13,328
Issuance of restricted shares	0	$ 13	(13)
Forfeitures of restricted shares (in shares)		(40,423)
Forfeitures of restricted shares	(524)	$ (40)	(484)
Proceeds from exercise of stock options	0
Share-based compensation	807		807
Purchase of treasury shares (in shares)						296,630
Purchase of treasury shares	(10,563)					$ (10,563)
Net income	38,904			38,904
Dividends on common shares	(4,727)			(4,727)
Other comprehensive income (loss) during the period	17,640				17,640
Ending balance (in shares) at Jun. 30, 2019		49,099,332				1,837,748
Ending balance at Jun. 30, 2019	1,537,121	$ 49,099	1,053,500	446,182	16,462	$ (28,122)
Beginning balance (in shares) at Dec. 31, 2019		71,499,829				1,995,996
Beginning balance at Dec. 31, 2019	2,469,582	$ 71,500	1,907,108	507,950	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 shares	(20,856)			(20,856)
Other comprehensive income (loss) during the period	21,618				21,618
Ending balance (in shares) at Jun. 30, 2020		71,674,087				2,211,305
Ending balance at Jun. 30, 2020	2,460,130	$ 71,674	1,909,839	481,948	39,613	$ (42,944)
Beginning balance (in shares) at Mar. 31, 2020		71,651,986				2,210,712
Beginning balance 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 shares	(10,441)			(10,441)
Other comprehensive income (loss) during the period	62				62
Ending balance (in shares) at Jun. 30, 2020		71,674,087				2,211,305
Ending balance at Jun. 30, 2020	$ 2,460,130	$ 71,674	$ 1,909,839	$ 481,948	$ 39,613	$ (42,944)