Basis of Presentation (Stock-Based Compensation) (Details) (USD $)	3 Months Ended		12 Months Ended			12 Months Ended	0 Months Ended		3 Months Ended		0 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2008	Mar. 31, 2013 Long-Term Incentive Plan 2012 [Member]	Mar. 31, 2013 Long-Term Incentive Plan 2005	Dec. 31, 2008 Stock Option	Jan. 22, 2013 Restricted Stock Units (RSUs) Long-Term Incentive Plan 2005	Jan. 17, 2012 Restricted Stock Units (RSUs) Long-Term Incentive Plan 2005	Mar. 31, 2013 Restricted Stock Units (RSUs) Long-Term Incentive Plan 2005 equal_installments	Mar. 31, 2013 Restricted Stock Units (RSUs) Long-Term Incentive Plan 2005 Grants Made in 2012	Jan. 22, 2013 Performance-Based Restricted Stock Units Long-Term Incentive Plan 2005	Jan. 17, 2012 Performance-Based Restricted Stock Units Long-Term Incentive Plan 2005	Dec. 31, 2008 Period One Stock Option	Dec. 31, 2008 Period Two Stock Option	Dec. 31, 2008 Period Three Stock Option
Stock-Based Compensation
Number of shares for issuance under future awards				396,469
Typical options expiration period after date of grant			10 years
Share-based compensation, award service periods						5 years
Share-based compensation, award vesting periods									5 years				3 years	4 years	5 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at January 1 (in shares)	377,907	570,762
Shares Granted (in shares)	0	0
Shares Exercised (in shares)	(9,835)	(12,500)
Shares Forfeited (in shares)	(1,800)	(5,250)
Outstanding at March 31 (in shares)	366,272	553,012
Options exercisable at March 31 (in shares)	366,272	505,295
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)	$ 22.62	$ 21.06
Weighted-Average Exercise Price, Granted (in dollars per share)	$ 0.00	$ 0.00
Weighted-Average Exercise Price, Exercised (in dollars per share)	$ 16.69	$ 9.89
Weighted-Average Exercise Price, Forfeited (in dollars per share)	$ 26.68	$ 20.62
Weighted-Average Exercise Price, Outstanding at March 31 (in dollars per share)	$ 22.76	$ 21.32
Weighted-Average Exercise Price, Options exercisable at March 31 (in dollars per share)	$ 22.76	$ 21.58
Vested options, weighted average remaining contractual life	3 years 4 months 10 days
Intrinsic value for vested options	$ 1,400,000
Intrinsic value for the total of all options exercised	84,000
Maximum exercise period	10 years
Cash received from options exercised	164,000	124,000
Tax benefit from options exercised	16,000	23,000
Equity instruments other than options, granted (in shares)							72,595	94,001			40,990	49,801
Award vesting, number of equal installments									3
Award, employee age threshold									62 years
Years of service required to vest after retirement										5 years
Share-based compensation costs	989,000	759,000
Share-based unrecognized compensation costs					$ 4,900,000