Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance (shares) at Dec. 31, 2014		31,545,145
Beginning Balance at Dec. 31, 2014	$ 711,651	$ 163,281	$ (22,128)	$ 345,213	$ 232,883	$ (7,598)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	68,014				68,014
Other comprehensive income (loss)	(1,937)					(1,937)
Comprehensive income	66,077
Cash dividends	(24,557)				(24,557)
Common stock issued in connection with an acquisition (shares)		8,635,879
Common stock issued in connection with an acquisition	281,530	$ 43,179		238,351
Repurchase of shares in connection with an acquisition related to stock-based compensation awards (shares)		(18,635)
Repurchase of shares in connection with an acquisition related to stock-based compensation awards	(608)		(608)
Issuance of common stock for stock-based compensation awards (shares)		130,902
Issuance of common stock for stock-based compensation awards	(1,722)		351	(2,073)
Stock-based compensation expense	4,435			4,435
Other, net	12			12
Ending Balance (shares) at Dec. 31, 2015		40,293,291
Ending Balance at Dec. 31, 2015	1,036,818	$ 206,460	(22,385)	585,938	276,340	(9,535)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	90,930				90,930
Other comprehensive income (loss)	(6,369)					(6,369)
Comprehensive income	84,561
Cash dividends	(29,734)				(29,734)
Common stock issued in connection with an acquisition (shares)		1,680,021
Common stock issued in connection with an acquisition	55,290	$ 8,400		46,890
Common stock issued in public offering (shares)		2,135,000
Common stock issued in public offering	84,105	$ 10,675		73,430
Issuance of common stock for stock-based compensation awards (shares)		223,961
Issuance of common stock for stock-based compensation awards	(1,652)		693	(2,345)
Stock-based compensation expense	3,117			3,117
Shares vested through Heritage acquisition	378			378
Ending Balance (shares) at Dec. 31, 2016		44,332,273
Ending Balance at Dec. 31, 2016	1,232,883	$ 225,535	(21,692)	707,408	337,536	(15,904)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	92,188				92,188
Other comprehensive income (loss)	7,439					7,439
Comprehensive income	99,627
Reclassification of the income tax effects of the Tax Cuts and Jobs Act to Retained earnings	0				2,046	(2,046)
Cash dividends	(34,416)				(34,416)
Common stock issued in connection with an acquisition (shares)		4,883,182
Common stock issued in connection with an acquisition	213,590	$ 24,416		189,174
Issuance of common stock for stock-based compensation awards (shares)		105,776
Issuance of common stock for stock-based compensation awards	(2,190)		1,786	(3,976)
Stock-based compensation expense	5,293			5,293
Shares vested through Heritage acquisition	196			196
Ending Balance (shares) at Dec. 31, 2017		49,321,231
Ending Balance at Dec. 31, 2017	$ 1,514,983	$ 249,951	$ (19,906)	$ 898,095	$ 397,354	$ (10,511)