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, 2016		36,377,807				1,456,333
Balance at beginning of period at Dec. 31, 2016		$ 36,378	$ 410,276	$ 214,454	$ (1,058)	$ (13,613)
Cumulative effect of change in accounting for derivatives at Dec. 31, 2016				0
Adjusted balance at beginning of period at Dec. 31, 2016				214,454	(1,058)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification to retained earnings due to change in federal corporate tax rate				0	0
Share-based compensation			2,419
Issuance of common stock (in shares)		2,141,072
Issuance of common stock		$ 2,141	92,359
Issuance of restricted shares (in shares)		84,147
Issuance of restricted shares		$ 84	(84)
Cancellation of restricted shares (in shares)		(472)
Cancellation of restricted shares		$ 0
Exercise of stock options (in shares)		103,356
Proceeds from exercise of stock options		$ 103	1,809
Net income	$ 64,398			64,398
Dividends on common shares				(11,158)
Other comprehensive income (loss) during the period	4,299				4,299
Purchase of treasury shares (in shares)						18,528
Purchase of treasury shares						$ (886)
Balance at end of period (in shares) at Sep. 30, 2017		38,705,910				1,474,861
Balance at end of period at Sep. 30, 2017	801,921	$ 38,706	506,779	267,694	3,241	$ (14,499)
Balance at beginning of period (in shares) at Dec. 31, 2017		38,734,873				1,474,861
Balance at beginning of period at Dec. 31, 2017	804,479	$ 38,735	508,404	273,119	(1,280)	$ (14,499)
Cumulative effect of change in accounting for derivatives at Dec. 31, 2017				28
Adjusted balance at beginning of period at Dec. 31, 2017	(1,672)			273,539	(1,672)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification to retained earnings due to change in federal corporate tax rate	(392)			392	(392)
Share-based compensation			4,652
Issuance of common stock (in shares)		10,124,491
Issuance of common stock		$ 10,124	537,003
Issuance of restricted shares (in shares)		85,855
Issuance of restricted shares		$ 86	(86)
Cancellation of restricted shares (in shares)		(472)
Cancellation of restricted shares		$ 0
Exercise of stock options (in shares)		67,203
Proceeds from exercise of stock options		$ 67	779
Net income	77,491			77,491
Dividends on common shares				(12,680)
Other comprehensive income (loss) during the period	(14,904)				(14,904)
Purchase of treasury shares (in shares)						40,123
Purchase of treasury shares						$ (2,062)
Balance at end of period (in shares) at Sep. 30, 2018		49,011,950				1,514,984
Balance at end of period at Sep. 30, 2018	$ 1,404,977	$ 49,012	$ 1,050,752	$ 338,350	$ (16,576)	$ (16,561)