Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Common Stock Issuable	Capital Surplus	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive (Loss) Income
Beginning balance at Dec. 31, 2016	$ 1,075,735	$ 70,899	$ 7,327	$ 1,275,849	$ (251,857)	$ (26,483)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	67,821				67,821
Other comprehensive income (loss)	3,269					3,269
Common stock issued to Dividend Reinvestment Plan and employee benefit plans (83,557 common shares in 2019, 25,248 common shares in 2018, 17,826 common shares in 2017)	450	18		432
Common stock issued for acquisitions (1,443,987 common shares in 2018, 6,515,505 common shares in 2017)	179,465	6,516		172,949
Amortization of stock options and restricted stock unit awards	5,827			5,827
Vesting of restricted stock unit awards, net of shares withheld to cover payroll taxes (109,100 common shares issued and 55,271 common shares deferred in 2019, 125,067 common shares issued and 99,779 common shares deferred in 2018, 114,837 common shares issued and 111,090 common shares deferred in 2017)	(1,594)	115	1,763	(3,472)
Deferred compensation plan, net, including dividend equivalents	361		361
Shares issued from deferred compensation plan (74,490 shares in 2019, 48,214 shares in 2018, 32,279 shares in 2017)	(107)	32	(368)	229
Common stock dividends ($0.68 per share in 2019, $0.58 per share in 2018, $0.38 per share in 2017)	(28,330)				(28,330)
Reclassification of disproportionate tax effects resulting from the Tax Cuts and Jobs Act of 2017 pursuant to ASU 2018-02	0				2,027	(2,027)
Ending balance at Dec. 31, 2017	1,303,334	77,580	9,083	1,451,814	(209,902)	(25,241)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	166,111				166,111
Other comprehensive income (loss)	(16,348)					(16,348)
Common stock issued to Dividend Reinvestment Plan and employee benefit plans (83,557 common shares in 2019, 25,248 common shares in 2018, 17,826 common shares in 2017)	679	25		654
Common stock issued for acquisitions (1,443,987 common shares in 2018, 6,515,505 common shares in 2017)	45,746	1,444		44,302
Amortization of stock options and restricted stock unit awards	6,057			6,057
Exercise of stock options (13,000 shares in 2019, 12,000 shares in 2018)	142	12		130
Vesting of restricted stock unit awards, net of shares withheld to cover payroll taxes (109,100 common shares issued and 55,271 common shares deferred in 2019, 125,067 common shares issued and 99,779 common shares deferred in 2018, 114,837 common shares issued and 111,090 common shares deferred in 2017)	(1,988)	125	1,931	(4,044)
Deferred compensation plan, net, including dividend equivalents	459		459
Shares issued from deferred compensation plan (74,490 shares in 2019, 48,214 shares in 2018, 32,279 shares in 2017)	(10)	48	(729)	671
Common stock dividends ($0.68 per share in 2019, $0.58 per share in 2018, $0.38 per share in 2017)	(46,628)				(46,628)
Ending balance at Dec. 31, 2018	1,457,554	79,234	10,744	1,499,584	(90,419)	(41,589)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	185,721				185,721
Other comprehensive income (loss)	49,983					49,983
Common stock issued to Dividend Reinvestment Plan and employee benefit plans (83,557 common shares in 2019, 25,248 common shares in 2018, 17,826 common shares in 2017)	2,193	83		2,110
Amortization of stock options and restricted stock unit awards	9,360			9,360
Exercise of stock options (13,000 shares in 2019, 12,000 shares in 2018)	212	13		199
Vesting of restricted stock unit awards, net of shares withheld to cover payroll taxes (109,100 common shares issued and 55,271 common shares deferred in 2019, 125,067 common shares issued and 99,779 common shares deferred in 2018, 114,837 common shares issued and 111,090 common shares deferred in 2017)	(1,442)	109	1,476	(3,027)
Deferred compensation plan, net, including dividend equivalents	525		525
Shares issued from deferred compensation plan (74,490 shares in 2019, 48,214 shares in 2018, 32,279 shares in 2017)	(244)	75	(1,254)	935
Common stock dividends ($0.68 per share in 2019, $0.58 per share in 2018, $0.38 per share in 2017)	(54,601)				(54,601)
Purchases of common stock (500,495 shares)	(13,020)	(500)		(12,520)
Ending balance at Dec. 31, 2019	$ 1,635,692	$ 79,014	$ 11,491	$ 1,496,641	$ 40,152	$ 8,394