Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Capital in Excess of Par Value	Accumulated Other Comprehensive (Loss) Income	Retained Earnings	Treasury Stock
Beginning Balance (in shares) at Dec. 31, 2014			55,697,124
Beginning Balance at Dec. 31, 2014		$ 489,051	$ 557	$ 201,130	$ 3,500	$ 523,099	$ (239,235)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		53,533				53,533
Other comprehensive income (loss)		(2,804)			(2,804)
Cash dividend, per share		(6,002)				(6,002)
Issuance of common stock including proceeds from exercise of common stock options (in shares)			248,121
Issuance of common stock including proceeds from exercise of common stock options		4,050	$ 3	4,047
Stock-based compensation expense		2,957		2,957
Acquisition		71,345		48,301			23,044
Repurchases of common stock		(31,659)					(31,659)
Ending Balance (in shares) at Dec. 31, 2015			55,945,245
Ending Balance at Dec. 31, 2015		580,471	$ 560	256,435	696	570,630	(247,850)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		64,080				64,080
Other comprehensive income (loss)		(8,313)			(8,313)
Cash dividend, per share		(7,632)				(7,632)
Issuance of common stock including proceeds from exercise of common stock options (in shares)			265,853
Issuance of common stock including proceeds from exercise of common stock options		1,900	$ 2	1,898
Stock-based compensation expense		2,790		2,790
Acquisition (in shares)			1,806,748
Acquisition		68,352	$ 18	68,334			0
Repurchases of common stock		(14,312)					(14,312)
Treasury share adjustment (in shares)	[1]		(2,022,627)
Ending Balance (in shares) at Dec. 31, 2016			55,995,219
Ending Balance at Dec. 31, 2016		687,336	$ 580	329,457	(7,617)	627,078	(262,162)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		50,244				50,244
Other comprehensive income (loss)		1,125
Loans transferred to portfolio from held-for-sale at fair value		1,125			1,125
Cash dividend, per share		(9,425)				(9,425)
Reclassification due to the adoption of ASU No. 2018-02		0			(1,660)	1,660
Issuance of common stock including proceeds from exercise of common stock options (in shares)			284,308
Issuance of common stock including proceeds from exercise of common stock options		3,421	$ 3	3,418
Stock-based compensation expense		3,396		3,396
Repurchases of common stock		(11,752)	$ (20)				(11,732)
Ending Balance (in shares) at Dec. 31, 2017			56,279,527.000
Ending Balance at Dec. 31, 2017		$ 724,345	$ 563	$ 336,271	$ (8,152)	$ 669,557	$ (273,894)

[1] The 2016 Consolidated Statement of Changes in Stockholder's Equity reflects an adjustment between shares issued and treasury stock. This reclassification had no impact on shares outstanding, earnings per share or retained earnings.