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
Balance at beginning of period (in shares) at Dec. 31, 2018		49,014,925				1,514,984
Balance at beginning of period 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)		103,794
Issuance of restricted shares	915	$ 103	812
Proceeds from exercise of stock options (in shares)		7,708
Proceeds from exercise of stock options	54	$ 8	46
Share-based compensation	748		748
Purchase of treasury shares (in shares)						26,134
Purchase of treasury shares	(998)					$ (998)
Net income	39,905			39,905
Dividends on common shares	(4,759)			(4,759)
Other comprehensive income (loss) during the period	3,648				3,648
Balance at end of period (in shares) at Mar. 31, 2019		49,126,427				1,541,118
Balance at end of period at Mar. 31, 2019	1,495,584	$ 49,126	1,053,190	412,005	(1,178)	$ (17,559)
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	$ 71,500	1,907,108	507,950	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 on common shares	(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)