Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock	Value of Shares Held in Rabbi Trust at Cost	Deferred Compensation Obligation	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2009	$ 412,649	$ 209	$ (2,482)	$ 2,482	$ 225,088	$ 184,599	$ 2,753
Beginning balance (in shares) at Dec. 31, 2009		21,072,196
Net income	40,240					40,240
Other comprehensive loss	(3,519)						(3,519)
Common dividend declared	(15,261)					(15,261)
Proceeds from exercise of stock options, net of cash paid	743	1				742
Proceeds from exercise of stock options (in shares)		44,930
Tax benefit related to equity award activity	68				68
Stock based compensation	1,666				1,666
Restricted stock awards issued, net of awards surrendered	(114)				(114)
Restricted stock awards issued, net of awards surrendered (in shares)		103,675
Deferred compensation obligation			(256)	256
Ending balance at Dec. 31, 2010	436,472	210	(2,738)	2,738	226,708	210,320	(766)
Ending balance (in shares) at Dec. 31, 2010		21,220,801
Net income	45,436					45,436
Other comprehensive loss	(3,720)						(3,720)
Common dividend declared	(16,304)					(16,304)
Proceeds from exercise of stock options, net of cash paid	4,127	2			4,125
Proceeds from exercise of stock options (in shares)		186,518
Tax benefit related to equity award activity	20				20
Stock based compensation	2,483				2,483
Restricted stock awards issued, net of awards surrendered	(361)				(361)
Restricted stock awards issued, net of awards surrendered (in shares)		60,495
Shares issued under direct stock purchase plan	824	1			823
Shares issued under direct stock purchase plan (in shares)		31,954
Deferred compensation obligation			(242)	242
Tax benefit related to deferred compensation distributions	80				80
Ending balance at Dec. 31, 2011	469,057	213	(2,980)	2,980	233,878	239,452	(4,486)
Ending balance (in shares) at Dec. 31, 2011	21,499,768	21,499,768
Net income	42,627					42,627
Other comprehensive loss	(40)						(40)
Common dividend declared	(18,408)					(18,408)
Common stock issued for acquisition	30,389	11			30,378
Common stock issued for acquisition (in shares)		1,068,514
Proceeds from exercise of stock options, net of cash paid	1,108	1			1,107
Proceeds from exercise of stock options (in shares)	(251,425)	61,326
Tax benefit related to equity award activity	426				426
Stock based compensation	2,845				2,845
Restricted stock awards issued, net of awards surrendered	(467)				(467)
Restricted stock awards issued, net of awards surrendered (in shares)		86,254
Shares issued under direct stock purchase plan	1,691				1,691
Shares issued under direct stock purchase plan (in shares)		58,147
Deferred compensation obligation			(199)	199
Tax benefit related to deferred compensation distributions	92				92
Ending balance at Dec. 31, 2012	$ 529,320	$ 225	$ (3,179)	$ 3,179	$ 269,950	$ 263,671	$ (4,526)
Ending balance (in shares) at Dec. 31, 2012	22,774,009	22,774,009