Consolidated Statements of Changes in Stockholders Equity (Unaudited) - USD ($) $ in Thousands		Total	Common Stock	Capital in Excess of Par Value	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Beginning Balance at Dec. 31, 2015		$ 580,471	$ 560	$ 256,435	$ 696	$ 570,630	$ (247,850)
Beginning Balance (in shares) at Dec. 31, 2015			55,945,245
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		45,970				45,970
Other comprehensive income		13,163			13,163
Cash dividend		(5,437)				(5,437)
Issuance of common stock including proceeds from exercise of common stock options		1,890	$ 2	1,888
Issuance of common stock including proceeds from exercise of common stock options (in shares)			174,211
Stock-based compensation expense		2,066		2,066
Stock Issued During Period, Shares, Acquisitions			1,806,748
Acquisition of Penn Liberty		66,777	$ 18	66,759
Repurchase of common stock		(12,890)					(12,890)
Treasury share reclassification (in shares)	[1]		(2,022,627)
Ending Balance at Sep. 30, 2016		692,010	$ 580	327,148	13,859	611,163	(260,740)
Ending Balance (in shares) at Sep. 30, 2016			55,903,577
Beginning Balance at Jun. 30, 2016					15,677
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		12,722
Other comprehensive income		(1,818)
Ending Balance at Sep. 30, 2016		692,010	$ 580	327,148	13,859	611,163	(260,740)
Ending Balance (in shares) at Sep. 30, 2016			55,903,577
Beginning Balance at Dec. 31, 2016		687,336	$ 580	329,457	(7,617)	627,078	(262,162)
Beginning Balance (in shares) at Dec. 31, 2016			55,995,219
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		60,076				60,076
Other comprehensive income		4,494			4,494
Cash dividend		(6,600)				(6,600)
Issuance of common stock including proceeds from exercise of common stock options		2,317	$ 2	2,315
Issuance of common stock including proceeds from exercise of common stock options (in shares)			222,424
Stock-based compensation expense		2,449		2,449
Repurchase of common stock		(9,211)	$ (20)				(9,191)
Ending Balance at Sep. 30, 2017		740,861	$ 562	334,221	(3,123)	680,554	(271,353)
Ending Balance (in shares) at Sep. 30, 2017			56,217,643
Beginning Balance at Jun. 30, 2017					(3,858)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		20,569
Other comprehensive income		735
Ending Balance at Sep. 30, 2017		$ 740,861	$ 562	$ 334,221	$ (3,123)	$ 680,554	$ (271,353)
Ending Balance (in shares) at Sep. 30, 2017			56,217,643

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