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, 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 (loss)	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)
Beginning balance at Dec. 31, 2013	591,540	23,805,984	235	(3,404)	3,404	305,179	293,560	(7,434)
Net income	13,383						13,383
Other comprehensive income (loss)	2,380							2,380
Common dividend declared	(5,725)						(5,725)
Proceeds from exercise of stock options	133	7,911				133
Tax benefit related to equity award activity	193					193
Equity based compensation	677					677
Restricted stock awards issued, net of awards surrendered	(472)	55,761	1			(473)
Shares issued under direct stock purchase plan	319	8,400				319
Deferred compensation obligation				(52)	52
Tax benefit related to deferred compensation distributions	128					128
Ending balance at Mar. 31, 2014	$ 602,556	$ 23,878,056	$ 236	$ (3,456)	$ 3,456	$ 306,156	$ 301,218	$ (5,054)