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, 2010	$ 436,472	$ 21,220,801	$ 210	$ (2,738)	$ 2,738	$ 226,708	$ 210,320	$ (766)
NET INCOME	34,267						34,267
OTHER COMPREHENSIVE INCOME (LOSS)	(3,594)
COMMON DIVIDEND DECLARED	(12,218)						(12,218)
PROCEEDS FROM EXERCISE OF STOCK OPTIONS	3,713	164,100	2			3,711
TAX BENEFIT RELATED TO EQUITY AWARD ACTIVITY	251					251
EQUITY BASED COMPENSATION	1,917					1,917
RESTRICTED STOCK AWARDS GRANTED, NET OF AWARDS	(361)	60,495				(361)
SHARES ISSUED UNDER DIRECT STOCK PURCHASE PLAN	540	19,713				540
DEFERRED COMPENSATION OBLIGATION				(146)	146
TAX BENEFIT RELATED TO DEFERRED COMPENSATION DISTRIBUTIONS	79					79
Ending balance at Sep. 30, 2011	461,066	21,465,109	212	(2,884)	2,884	232,845	232,369	(4,360)
Beginning balance at Dec. 31, 2011	469,057	21,499,768	213	(2,980)	2,980	233,878	239,452	(4,486)
NET INCOME	32,658						32,658
OTHER COMPREHENSIVE INCOME (LOSS)	897							897
COMMON DIVIDEND DECLARED	(13,629)						(13,629)
PROCEEDS FROM EXERCISE OF STOCK OPTIONS	953	48,976				953
TAX BENEFIT RELATED TO EQUITY AWARD ACTIVITY	153					153
EQUITY BASED COMPENSATION	2,178					2,178
RESTRICTED STOCK AWARDS GRANTED, NET OF AWARDS	(344)	85,254	1			(345)
SHARES ISSUED UNDER DIRECT STOCK PURCHASE PLAN	953	32,928				953
DEFERRED COMPENSATION OBLIGATION				(123)	123
TAX BENEFIT RELATED TO DEFERRED COMPENSATION DISTRIBUTIONS	89					89
Ending balance at Sep. 30, 2012	$ 492,965	$ 21,666,926	$ 214	$ (3,103)	$ 3,103	$ 237,859	$ 258,481	$ (3,589)