Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2014	$ 797,133	$ 32,774	$ 565,166	$ 231,646	$ (32,453)
Changes in Stockholders' Equity
Comprehensive income	64,593			61,326	3,267
Cash dividends declared and paid, $0.79 and $0.74 per share at September 30, 2016 and September 30, 2015, respectively	(26,981)			(26,981)
Issuance of common stock in business acquisitions	159,904	5,183	154,721
Stock issued - stock options	1,234	98	1,136
Shares issued – directors’ stock plans	316	11	305
Shares issued – restricted stock units	(343)	54	(397)
Share-based compensation	2,507	11	2,496
Ending Balance at Sep. 30, 2015	998,363	38,131	723,427	265,991	(29,186)
Beginning Balance at Jun. 30, 2015					(31,104)
Changes in Stockholders' Equity
Comprehensive income	26,385
Ending Balance at Sep. 30, 2015	998,363	38,131	723,427	265,991	(29,186)
Beginning Balance at Dec. 31, 2015	1,015,974	38,168	725,280	281,558	(29,032)
Changes in Stockholders' Equity
Comprehensive income	63,591			59,701	3,890
Cash dividends declared and paid, $0.79 and $0.74 per share at September 30, 2016 and September 30, 2015, respectively	(30,293)			(30,293)
Issuance of common stock in business acquisitions	1,504,811	32,074	1,472,737
Stock issued - stock options	998	100	898
Shares issued – directors’ stock plans	2,597	95	2,502
Shares issued – restricted stock units	(466)	60	(526)
Share-based compensation	6,454		6,454
Ending Balance at Sep. 30, 2016	2,563,666	70,497	2,207,345	310,966	(25,142)
Beginning Balance at Jun. 30, 2016					(25,698)
Changes in Stockholders' Equity
Comprehensive income	11,288
Ending Balance at Sep. 30, 2016	$ 2,563,666	$ 70,497	$ 2,207,345	$ 310,966	$ (25,142)