Consolidated Statements of Shareholders' Equity - 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, 2016		36,377,807				1,456,333
Balance at beginning of period at Dec. 31, 2016	$ 646,437	$ 36,378	$ 410,276	$ 214,454	$ (1,058)	$ (13,613)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)		2,141,072
Issuance of common stock	94,500	$ 2,141	92,359
Issuance of restricted shares (in shares)		84,147
Issuance of restricted shares	0	$ 84	(84)
Forfeitures of restricted shares (in shares)		(472)
Forfeitures of restricted shares	0
Exercise of stock options (in shares)		132,319
Exercise of stock options	2,669	$ 132	2,537
Share-based compensation	3,316		3,316
Purchase of treasury shares (in shares)						18,528
Purchase of treasury shares	(886)					$ (886)
Net income	73,548			73,548
Dividends on common shares	(14,883)			(14,883)
Other comprehensive income (loss) during the period	(222)				(222)
Balance at end of period (in shares) at Dec. 31, 2017		38,734,873				1,474,861
Balance at end of period at Dec. 31, 2017	804,479	$ 38,735	508,404	273,119	(1,280)	$ (14,499)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting	28			28
Issuance of common stock (in shares)		10,124,491
Issuance of common stock	547,127	$ 10,124	537,003
Issuance of restricted shares (in shares)		89,855
Issuance of restricted shares	0	$ 90	(90)
Forfeitures of restricted shares (in shares)		(10,580)
Forfeitures of restricted shares	0	$ (10)	10
Exercise of stock options (in shares)		76,286
Exercise of stock options	914	$ 76	838
Share-based compensation	5,419		5,419
Purchase of treasury shares (in shares)						40,123
Purchase of treasury shares	(2,062)					$ (2,062)
Net income	121,027			121,027
Dividends on common shares	(17,431)			(17,431)
Reclassification to retained earnings due to change in federal corporate tax rate				392	(392)
Other comprehensive income (loss) during the period	(3,154)				(3,154)
Balance at end of period (in shares) at Dec. 31, 2018		49,014,925				1,514,984
Balance at end 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]
Cumulative effect of change in accounting	(276)			(276)
Issuance of common stock (in shares)		22,181,522
Issuance of common stock	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)		(41,295)
Forfeitures of restricted shares	(559)	$ (41)	(518)
Exercise of stock options (in shares)		197,103
Exercise of stock options	5,139	$ 197	4,942
Share-based compensation	3,220		3,220
Purchase of treasury shares (in shares)						481,012
Purchase of treasury shares	(18,410)					$ (18,410)
Net income	161,441			161,441
Dividends on common shares	(30,350)			(30,350)
Other comprehensive income (loss) during the period	22,821				22,821
Balance at end of period (in shares) at Dec. 31, 2019		71,499,829				1,995,996
Balance at end of period at Dec. 31, 2019	$ 2,469,582	$ 71,500	$ 1,907,108	$ 507,950	$ 17,995	$ (34,971)