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
Common Stock, Dividends, Per Share, Declared								$ 1.04
Beginning balance at Dec. 31, 2014		$ 640,527		$ 237	$ (3,666)	$ 3,666	$ 311,978	$ 330,444	$ (2,132)
Beginning balance (in shares) at Dec. 31, 2014			23,998,738
Net income		64,960						64,960
Other comprehensive loss		(320)							(320)
Common dividend declared		(27,235)						(27,235)
Common stock issued for acquisition		86,415		21			86,394
Common stock issued for acquisition (in shares)			2,052,137
Proceeds from exercise of stock options, net of cash paid		1,367		1			1,366
Proceeds from exercise of stock options (in shares)			100,794
Tax benefit related to equity award activity		1,042					1,042
Stock based compensation		2,490					2,490
Restricted stock awards issued, net of awards surrendered (in shares)			23,851
Restricted stock awards issued, net of awards surrendered		(657)		1			(658)
Stock Issued During Period, Shares, Other			60,832
Stock Issued During Period, Value, Other		2,695					2,695
Increase (Decrease) in Deferred Compensation					(292)	292
Tax benefit related to deferred compensation distributions		179					179
Ending balance (in shares) at Dec. 31, 2015			26,236,352
Ending balance at Dec. 31, 2015		771,463		260	(3,958)	3,958	405,486	$ 368,169	(2,452)
Common Stock, Dividends, Per Share, Declared								$ 1.16
Net income		76,648						$ 76,648
Other comprehensive loss		1,115							1,115
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		0			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		0			(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)
Common Stock, Dividends, Per Share, Declared								$ 1.28
Net income		87,204						$ 87,204
Other comprehensive loss		(494)							(494)
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					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 and Other Retirement Benefits					(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)

[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.