Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive (Loss)/Income	Treasury Stock
Beginning Balance at Dec. 31, 2015	$ 792,237	$ 90,326	$ 210,545	$ 544,228	$ (16,457)	$ (36,405)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,093			16,093
Other comprehensive income (loss), net of tax	8,341				8,341
Cash dividends declared	(6,601)			(6,601)
Treasury stock issued for restricted awards	0			(2,491)		2,491
Recognition of restricted stock compensation expense	731		731
Ending Balance at Mar. 31, 2016	810,801	90,326	211,276	551,229	(8,116)	(33,914)
Beginning Balance at Dec. 31, 2016	841,956	90,326	213,098	585,891	(13,784)	(33,575)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,188			18,188
Other comprehensive income (loss), net of tax	1,188				1,188
Cash dividends declared	(6,960)			(6,960)
Treasury stock issued for restricted awards	(194)			(2,014)		1,820
Recognition of restricted stock compensation expense	1,002		1,002
Ending Balance at Mar. 31, 2017	$ 855,180	$ 90,326	$ 214,100	$ 595,105	$ (12,596)	$ (31,755)