Incentive Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Incentive Plans [Abstract]
Number of common shares available for grant under the incentive plan (in shares)	1,770,329
Number of shares of stock authorized for issuance under the Nonqualified Plan (in shares)	3,600,000
Stock option activity [Roll Forward]
Outstanding, beginning balance (in shares)	315,000
Granted (in shares)	0
Exercised (in shares)	(160,000)
Cancelled (in shares)	(3,000)
Outstanding, ending balance (in shares)	152,000	315,000
Exercisable, ending balance (in shares)	152,000
Weighted average exercise price [Abstract]
Outstanding, beginning balance (in dollars per share)	$ 16.67
Granted (in dollars per share)	$ 0
Exercised (in dollars per share)	$ 14.05
Cancelled (in dollars per share)	$ 25.99
Outstanding, ending balance (in dollars per share)	$ 19.30	$ 16.67
Exercisable, ending balance (in dollars per share)	$ 19.30
Weighted average remaining contractual life, stock option awards outstanding at end of year (in years)	3 years 3 months 18 days
Weighted average remaining contractual life, stock option awards exercisable at end of year (in years)	3 years 3 months 18 days
Aggregate intrinsic value of options outstanding, ending balance	$ 2,019,000
Aggregate intrinsic value of options exercisable ending balance	2,019,000
Intrinsic value of options exercised during the year	2,500,000	2,200,000	2,000,000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	9,814,000	8,601,000	8,126,000
Weighted average grant date fair value of restricted stock awards during the year (in dollars per share)	$ 30.47
Restricted stock awards activity [Roll Forward]
Non-vested, beginning balance (in shares)	778,000
Granted (in shares)	375,000
Vested (in shares)	(383,000)
Cancelled/Forfeited (in shares)	(19,000)
Non-vested, ending balance (in shares)	751,000	778,000
Weighted-average market value [Abstract]
Non-vested, beginning balance (in dollars per share)	$ 23.91
Granted (in dollars per share)	$ 30.47
Vested (in dollars per share)	$ 22.65
Cancelled/forfeited (in dollars per share)	$ 28.51
Non-vested, ending balance (in dollars per share)	$ 27.70	$ 23.91
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	9,814,000	8,601,000	8,126,000
Tax benefits (expense) associated with stock-based compensation	4,000,000	3,400,000	3,300,000
Fair value of shares vested during the year	11,700,000	11,100,000	6,700,000
Weighted average grant date fair value of restricted stock awards during the year (in dollars per share)	$ 30.47	$ 29.47	$ 17.55
Unrecognized compensation expense associated with the unvested shares outstanding	$ 12,200,000
Unrecognized compensation expense, period for recognition (in months)	22 months
Weighted-average market value [Abstract]
Granted (in dollars per share)	$ 30.47	$ 29.47	$ 17.55
Restricted Stock Awards [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	3 years
Restricted Stock Awards [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	5 years