Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Total		Common Stock Outstanding	Common Stock	Value of Shares Held in Rabbi Trust at Cost	Deferred Compensation Obligation	Additional Paid in Capital	Retained Earnings		Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2015		$ 771,463			$ 260	$ (3,958)	$ 3,958	$ 405,486	$ 368,169		$ (2,452)
Beginning balance (in shares) at Dec. 31, 2015				26,236,352
Net income		76,648							$ 76,648
Other comprehensive income		1,115									1,115
Common Stock, Dividends, Per Share, Declared									$ 1.16
Common dividend declared		(30,722)							$ (30,722)
Common stock issued for acquisition		40,730			7			40,723
Common stock issued for acquisition (in shares)				672,665
Proceeds from exercise of stock options, net of cash paid		201						201
Proceeds from exercise of stock options (in shares)				13,449
Tax benefit related to equity award activity		476						476
Stock based compensation		2,965						2,965
Restricted stock awards issued, net of awards surrendered (in shares)				33,432
Restricted stock awards issued, net of awards surrendered		(696)			1			(697)
Stock Issued During Period, Shares, Other				49,915
Stock Issued During Period, Value, Other		2,323						2,323
Increase (Decrease) in Deferred Compensation						(319)	319
Tax benefit related to deferred compensation distributions		187						187
Ending balance (in shares) at Dec. 31, 2016				27,005,813
Ending balance at Dec. 31, 2016		864,690			268	(4,277)	4,277	451,664	414,095		(1,337)
Net income		87,204							$ 87,204
Other comprehensive income		(494)									(494)
Common Stock, Dividends, Per Share, Declared									$ 1.28
Common dividend declared		(34,997)							$ (34,997)
Common stock issued for acquisition		23,468			4			23,464
Common stock issued for acquisition (in shares)				369,286
Proceeds from exercise of stock options, net of cash paid		214			0			214
Proceeds from exercise of stock options (in shares)				19,340
Stock based compensation		3,333						3,333
Restricted stock awards issued, net of awards surrendered (in shares)				31,665
Restricted stock awards issued, net of awards surrendered		(1,422)			1			(1,423)
Stock Issued During Period, Shares, Other				24,086
Stock Issued During Period, Value, Other		1,636						1,636
Increase (Decrease) in Deferred Compensation		0				(313)	313
Ending balance (in shares) at Dec. 31, 2017				27,450,190
Ending balance at Dec. 31, 2017		943,809			273	(4,590)	4,590	479,430	465,937		(1,831)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	[1]	177						542	(365)
Prior Period Reclassification Adjustment		0	[2]						397	[3]	(397)	[3]
Net income		121,622							$ 121,622
Other comprehensive income		1,886									1,886
Common Stock, Dividends, Per Share, Declared									$ 1.52
Common dividend declared		(42,051)							$ (42,051)
Common stock issued for acquisition		42,474			5			42,469
Common stock issued for acquisition (in shares)				528,353
Proceeds from exercise of stock options, net of cash paid		184						184
Proceeds from exercise of stock options (in shares)				23,195
Stock based compensation		4,225						4,225
Restricted stock awards issued, net of awards surrendered (in shares)				43,383
Restricted stock awards issued, net of awards surrendered		(1,371)			1			(1,372)
Stock Issued During Period, Shares, Other				35,287
Stock Issued During Period, Value, Other		2,712						2,712
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits						(128)	128
Ending balance (in shares) at Dec. 31, 2018				28,080,408
Ending balance at Dec. 31, 2018		1,073,490			$ 279	$ (4,718)	$ 4,718	$ 527,648	546,736		(1,173)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets		$ 0	[3]						$ 831	[2]	$ (831)	[2]

[1] Represents adjustment needed to reflect the cumulative impact on retained earnings for previously recognized stock based compensation, which included an adjustment for estimated forfeitures. Pursuant to the Company's adoption of Accounting Standards Update 2016-09, the Company has elected to recognize stock based compensation without inclusion of a forfeiture estimate, and as such has recognized this adjustment to present retained earnings consistent with this election.

[2] Represents adjustment needed to reflect the cumulative impact on retained earnings for the classification and measurement of investments in equity securities. Pursuant to the Company's adoption of Accounting Standards Update 2016-01, the Company's investments in equity securities will no longer be classified as available for sale, therefore the Company was required to reclassify the net unrealized gain recognized on the change in fair value of these equity securities from other comprehensive income to retained earnings.

[3] Represents adjustment needed to reflect the cumulative impact on retained earnings for reclassification of the income tax effects attributable to accumulated other comprehensive income, as a result of the Tax Cuts and Jobs Act (the "Tax Act"). Pursuant to the Company's adoption of Accounting Standards Update 2018-02, the Company has elected to reclassify amounts stranded in other comprehensive income to retained earnings.