Consolidated Statements of Stockholders' Equity (Unaudited) (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, 2011	$ 469,057	$ 21,499,768	$ 213	$ (2,980)	$ 2,980	$ 233,878	$ 239,452	$ (4,486)
Net income	12,183						12,183
Other comprehensive income	658
Common dividend declared	(4,538)						(4,538)
Proceeds from exercise of stock options	439	20,377				439
Tax benefit related to equity award activity	69					69
Equity based compensation	853					853
Restricted stock awards issued, net of awards surrendered	(229)	77,965				(229)
Shares issued under direct stock purchase plan	285	10,175				285
Deferred compensation obligation				(16)	16
Tax benefit related to deferred compensation distributions	86					86
Ending balance at Mar. 31, 2012	478,863	21,608,285	213	(2,996)	2,996	235,381	247,097	(3,828)
Beginning balance at Dec. 31, 2012	529,320	22,774,009	225	(3,179)	3,179	269,950	263,671	(4,526)
Net income	12,252						12,252
Other comprehensive income	57							57
Common dividend declared	(5,032)						(5,032)
Proceeds from exercise of stock options	451	17,450				451
Tax benefit related to equity award activity	166					166
Equity based compensation	760					760
Restricted stock awards issued, net of awards surrendered	(507)	79,636	1			(508)
Shares issued under direct stock purchase plan	8	252				8
Deferred compensation obligation				(19)	19
Tax benefit related to deferred compensation distributions	100					100
Ending balance at Mar. 31, 2013	$ 537,575	$ 22,871,347	$ 226	$ (3,198)	$ 3,198	$ 270,927	$ 270,891	$ (4,469)