Incentive Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Incentive Plans [Abstract]
Number of common shares available for grant under the incentive plan (in shares)	818,655
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)	603,000
Granted (in shares)	16,000
Exercised (in shares)	(208,000)
Cancelled (in shares)	(96,000)
Outstanding, ending balance (in shares)	315,000	603,000
Exercisable, ending balance (in shares)	315,000
Weighted average exercise price [Abstract]
Outstanding, beginning balance (in dollars per share)	$ 18.20
Granted (in dollars per share)	$ 30.59
Exercised (in dollars per share)	$ 19.00
Cancelled (in dollars per share)	$ 23.48
Outstanding, ending balance (in dollars per share)	$ 16.67	$ 18.20
Exercisable, ending balance (in dollars per share)	$ 16.67
Weighted average remaining contractual life, stock option awards outstanding at end of year (in years)	2.9
Weighted average remaining contractual life, stock option awards exercisable at end of year (in years)	2.9
Aggregate intrinsic value of options outstanding, ending balance	$ 2,913,000
Aggregate intrinsic value of options exercisable ending balance	2,913,000
Intrinsic value of options exercised during the year	2,200,000	2,000,000	1,900,000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period, minimum (in years)	3Y
Stock awards vesting period, maximum (in years)	5Y
Share-based compensation expense	8,601,000	8,126,000	10,064,000
Fair value of shares vested during the year	11,100,000	6,700,000	6,900,000
Weighted average grant date fair value of restricted stock awards during the year (in dollars per share)	$ 29.47	$ 17.55	$ 20.92
Restricted stock awards activity [Roll Foward]
Non-vested, beginning balance (in shares)	775,000
Granted (in shares)	408,000
Vested (in shares)	(380,000)
Cancelled/Forfeited (in shares)	(25,000)
Non-vested, ending balance (in shares)	778,000	775,000
Weighted-average market value [Abstract]
Non-vested, beginning balance (in dollars per share)	$ 19.43
Granted (in dollars per share)	$ 29.47	$ 17.55	$ 20.92
Vested (in dollars per share)	$ 20.94
Cancelled/forfeited (in dollars per share)	$ 20.99
Non-vested, ending balance (in dollars per share)	$ 23.91	$ 19.43
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	8,600,000	8,100,000	10,100,000
Unrecognized compensation expense	11,200,000
Unrecognized compensation expense, period for recognition (in months)	23
Tax benefits (expense) associated with stock-based compensation	3,400,000	3,300,000	4,200,000
Unrecognized compensation expense associated with the unvested shares outstanding	$ 11,200,000