CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - 9 months ended Sep. 30, 2017 - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]	Deferred Compensation Arrangements [Member]	Total
Balance at Dec. 31, 2016	$ 44,950	$ 545,775	$ 614,692	$ 7,843	$ (15,160)	$ 0	$ 1,198,100
Balance (in shares) at Dec. 31, 2016	44,437,415
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			78,691				78,691
Other comprehensive income, net of tax				8,334			8,334
Cash dividends declared:
Common, $0.98 per share			(48,203)				(48,203)
Common stock issued under employee stock ownership plan	$ 238	3,502					3,740
Common stock issued under employee stock ownership plan (in shares)	237,525
Stock-based compensation		3,985					3,985
Stock issued for acquisitions	$ 6,006	334,731					340,737
Stock issued for acquisitions (in shares)	6,006,301
Deferred compensation arrangements acquired					(10,022)	10,022	0
Deferred compensation arrangements acquired (in shares)	(179,003)
Treasury stock issued to benefit plans, net		1,893			2,742	3,226	7,861
Treasury stock issued to benefit plans, net (in shares)	84,890
Balance at Sep. 30, 2017	$ 51,194	$ 889,886	$ 645,180	$ 16,177	$ (22,440)	$ 13,248	$ 1,593,245
Balance (in shares) at Sep. 30, 2017	50,587,128