Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance at Dec. 31, 2013	$ 696,500	$ 29,790	$ 488,177	$ 199,053	$ (20,520)
Changes in Stockholders' Equity [Roll Forward]
Comprehensive income	32,581			30,049	2,532
Cash dividends declared per share: $0.48 and $0.46 per share for the six months ended June 30, 2015 and June 30, 2014, respectively	(13,769)			(13,769)
Stock Issued During Period, Value, New Issues	76,175	2,875	73,300
Stock issued - stock options	854	41	813
Shares issued – directors’ stock plans	468	18	450
Shares issued – restricted stock units	(484)	$ 36	(520)
Share-based compensation	1,173		1,173
Ending Balance at Jun. 30, 2014	793,498	$ 32,760	563,393	215,333	(17,988)
Beginning Balance at Dec. 31, 2014	797,133	32,774	565,166	231,646	(32,453)
Changes in Stockholders' Equity [Roll Forward]
Comprehensive income	38,208			36,859	1,349
Cash dividends declared per share: $0.48 and $0.46 per share for the six months ended June 30, 2015 and June 30, 2014, respectively	(17,049)			(17,049)
Stock Issued During Period, Value, Acquisitions	159,904	5,183	154,721
Stock issued - stock options	1,146	88	1,058
Shares issued – directors’ stock plans	316	11	305
Shares issued – restricted stock units	(328)	53	(381)
Share-based compensation	1,461	1	1,460
Ending Balance at Jun. 30, 2015	$ 980,791	$ 38,110	$ 722,329	$ 251,456	$ (31,104)