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, 2015		40,293,291
Beginning 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
Other, net	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
Other, net	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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	146,920				146,920
Other comprehensive income (loss)	(7,385)					(7,385)
Comprehensive income	139,535
Repurchase of shares in connection with stock repurchase program (in shares)		(199,065)
Repurchase of shares in connection with stock repurchase program	(7,062)		(7,062)
Cash dividends	(43,614)				(43,614)
Common stock issued in connection with an acquisition (shares)		9,306,477
Common stock issued in connection with an acquisition	434,519	$ 46,532		387,987
Repurchase of shares in connection with acquisition related to stock-based compensation awards (in shares)		(2,000)
Repurchase of shares in connection with acquisition related to stock-based compensation awards	(93)		(93)
Issuance of common stock for stock-based compensation awards (shares)		119,837
Issuance of common stock for stock-based compensation awards	(1,863)		2,816	(4,679)
Stock-based compensation expense	7,251			7,251
Other, net	257			257
Ending Balance (shares) at Dec. 31, 2018		58,546,480
Ending Balance at Dec. 31, 2018	$ 2,043,913	$ 296,483	$ (24,245)	$ 1,288,911	$ 500,660	$ (17,896)