Stock-based Compensation (Details) (USD $)	12 Months Ended									0 Months Ended		12 Months Ended	0 Months Ended		12 Months Ended				0 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2008	Dec. 31, 2008 Stock Option	Dec. 31, 2012 Long-Term Incentive Plan 2012	May 16, 2012 Long-Term Incentive Plan 2012	Dec. 31, 2012 Long-Term Incentive Plan 2005	Dec. 31, 2011 Long-Term Incentive Plan 2005	Jan. 17, 2012 Long-Term Incentive Plan 2005 Restricted Stock Units (RSUs)	Jan. 18, 2011 Long-Term Incentive Plan 2005 Restricted Stock Units (RSUs)	Dec. 31, 2012 Long-Term Incentive Plan 2005 Restricted Stock Units (RSUs) equal_installments	Jan. 17, 2012 Long-Term Incentive Plan 2005 Performance-Based Restricted Stock Units	Oct. 11, 2011 Long-Term Incentive Plan 2005 Performance-Based Restricted Stock Units	Dec. 31, 2012 Long-Term Incentive Plan 2005 Performance-Based Restricted Stock Units	Dec. 31, 2012 2006 ESPP	Dec. 31, 2011 2006 ESPP	Jan. 01, 2006 2006 ESPP	Jan. 01, 2006 2006 ESPP Minimum	Dec. 31, 2012 Grants Made in 2012 Long-Term Incentive Plan 2005 Restricted Stock Units (RSUs)	Dec. 31, 2012 Grants Made in 2012 Long-Term Incentive Plan 2005 Performance-Based Restricted Stock Units	Dec. 31, 2012 Grants Made in 2011 Long-Term Incentive Plan 2005 Restricted Stock Units (RSUs)	Dec. 31, 2012 Grants Made in 2011 Long-Term Incentive Plan 2005 Performance-Based Restricted Stock Units	Dec. 31, 2008 Period One Stock Option	Dec. 31, 2008 Period Two Stock Option	Dec. 31, 2008 Period Three Stock Option	Dec. 31, 2012 Directors	Dec. 31, 2011 Directors	Dec. 31, 2010 Directors	Dec. 31, 2012 Fair Market Value at Investment Date 2006 ESPP	Dec. 31, 2012 Fair Market Value at Closing Price 2006 ESPP	Dec. 31, 2011 Fair Market Value at Closing Price 2006 ESPP
Stock-Based Compensation
Maximum number of shares issuable (in shares)							500,000											500,000
Shares available for issuance (in shares)						509,884			321,894
Equity instruments other than options, granted (in shares)										94,001	101,150		49,801	21,200
Share-based compensation, award vesting periods												5 years												3 years	4 years	5 years
Award vesting, number of equal installments												3
Award, employee age threshold												62 years			62 years
Years of service required to vest after retirement																				5 years	5 years	10 years	10 years
Typical options expiration period after date of grant				10 years
Share-based compensation, award service periods					5 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares Outstanding at January 1 (in shares)	570,762	672,721	704,471
Shares Granted (in shares)	0	0	0
Shares Exercised (in shares)	(172,521)	(53,625)	(20,500)
Shares Forfeited (in shares)	(20,334)	(48,334)	(11,250)
Shares Outstanding at September 30 (in shares)	377,907	570,762	672,721
Options exercisable at September 30 (in shares)	333,024	436,245	399,071
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted-Average Exercise Price, Outstanding at January 1 (in dollars per share)	$ 21.06	$ 20.27	$ 20.02
Weighted-Average Exercise Price, Granted (in dollars per share)	$ 0.00	$ 0.00	$ 0.00
Weighted-Average Exercise Price, Exercised (in dollars per share)	$ 17.39	$ 9.65	$ 10.68
Weighted-Average Exercise Price, Forfeited (in dollars per share)	$ 23.42	$ 22.73	$ 21.63
Weighted-Average Exercise Price, Outstanding at September 30 (in dollars per share)	$ 22.62	$ 21.06	$ 20.27
Weighted-Average Exercise Price, Options exercisable (in dollars per share)	$ 23.16	$ 20.86	$ 18.80
Vested options, weighted average remaining contractual life	3 years 7 months 6 days
Intrinsic value for vested options	$ 1,700,000
Intrinsic value for the total of all options exercised	1,500,000
Fair value of shares under vested stock options and awards	2,200,000
Cash received from options exercised	3,000,000	517,000
Tax benefit from options exercised	222,000	108,000
Share-based compensation costs	2,200,000	1,300,000	926,000													151,000	39,000										90,000	83,000	87,000
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent																			85.00%											95.00%	100.00%	100.00%
Share-based unrecognized compensation costs								$ 2,900,000
Stock Issued During Period, Shares, Issued for Services																											5,200	5,200	5,000
Stocks purchased under the plan (in shares)																42,879	3,500