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, 2012	$ 529,320		$ 225	$ (3,179)	$ 3,179	$ 269,950	$ 263,671	$ (4,526)
Beginning balance (in shares) at Dec. 31, 2012		22,774,009
Net income	50,254						50,254
Other comprehensive loss	(2,908)							(2,908)
Common dividend declared	(20,365)						(20,365)
Common stock issued for acquisition	29,390		8			29,382
Common stock issued for acquisition (in shares)		818,650
Proceeds from exercise of stock options	2,475		1			2,474
Proceeds from exercise of stock options (in shares)		98,807
Tax benefit related to equity award activity	503					503
Stock based compensation	2,462					2,462
Restricted stock awards issued, net of awards surrendered (in shares)		86,331
Restricted stock awards issued, net of awards surrendered	(669)		1			(670)
Stock Issued During Period, Shares, Other		28,187
Stock Issued During Period, Value, Other	969					969
Increase (Decrease) in Deferred Compensation				(225)	225
Tax benefit related to deferred compensation distributions	109					109
Ending balance (in shares) at Dec. 31, 2013		23,805,984
Ending balance at Dec. 31, 2013	591,540		235	(3,404)	3,404	305,179	293,560	(7,434)
Net income	59,845						59,845
Other comprehensive loss	5,302							5,302
Common dividend declared	(22,961)						(22,961)
Common stock issued for acquisition	0
Proceeds from exercise of stock options	2,333		1			2,332
Proceeds from exercise of stock options (in shares)		91,171
Tax benefit related to equity award activity	704					704
Stock based compensation	2,712					2,712
Restricted stock awards issued, net of awards surrendered (in shares)		59,675
Restricted stock awards issued, net of awards surrendered	(641)		1			(642)
Stock Issued During Period, Shares, Other		41,908
Stock Issued During Period, Value, Other	1,555					1,555
Increase (Decrease) in Deferred Compensation	0			(262)	262
Tax benefit related to deferred compensation distributions	138					138
Ending balance (in shares) at Dec. 31, 2014		23,998,738
Ending balance at Dec. 31, 2014	640,527		237	(3,666)	3,666	311,978	330,444	(2,132)
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	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 and Other Retirement Benefits				(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)