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		90,251			86,830	3,421
Cash dividends declared		(36,918)			(36,918)
Issuance of common stock and common stock equivalents in business combinations		159,904	5,183	154,721
Net shares issued under share-based compensation plans		2,126	200	1,926
Share-based compensation expense		3,478	11	3,467
Ending balance at Dec. 31, 2015		1,015,974	38,168	725,280	281,558	(29,032)
Changes in Stockholders' Equity
Comprehensive income		97,028			108,032	(11,004)
Cash dividends declared		(49,389)			(49,389)
Issuance of common stock and common stock equivalents in business combinations		1,504,811	32,074	1,472,737
Net shares issued under share-based compensation plans		(350)	351	(701)
Share-based compensation expense		13,452	6	13,446
Ending balance at Dec. 31, 2016		2,581,526	70,599	2,210,762	340,201	(40,036)
Changes in Stockholders' Equity
Cumulative effect adjustment of change in accounting policy, net of tax impact		3,659			3,659
Comprehensive income		168,579			149,523	19,056
Cash dividends declared		(78,498)			(78,498)
Issuance of common stock and common stock equivalents in business combinations		0	0	0
Net shares issued under share-based compensation plans		(23,863)	608	(24,471)
Share-based compensation expense		17,346	0	17,346
Reclassification of certain income tax effects	[1]	0			4,518	(4,518)
Ending balance at Dec. 31, 2017		$ 2,668,749	$ 71,207	$ 2,203,637	$ 419,403	$ (25,498)

[1] The reclassification from accumulated other comprehensive income (loss) to retained earnings was due to the early adoption of ASU 2018-02, refer to Note 1 for further details on the adoption.