Stock Incentive Plans (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2011 Year Property State	Sep. 30, 2010
Summary of stock options activity
Stock options shares at beginning of year	1,207
Stock option, Weighted Average Exercise Price Beginning balance	$ 39.45
Stock option, Weighted Average Remaining Contract Life (years) Beginning of year	8.0
Options granted, number of shares	289
Options granted, Weighted Average Exercise Price	$ 49.17
Options exercised, number of shares	(153)
Option exercised, Weighted Average Exercise Price	$ 37.43
Option exercised, Aggregate Intrinsic Value	2,190,000	668,000
Options terminated, number of shares	(7)
Option terminated, Weighted Average Exercise Price	$ 43.02
Stock options shares at end of year	1,336
Stock option, Weighted Average Exercise Price Ending balance	$ 41.77
Stock option, Weighted Average Remaining Contract Life (years) end of year	7.8
Stock options, Aggregate Intrinsic Value End of year	14,255,000
Options exercisable at end of period, number of shares	506
Options exercisable at end of period Weighted Average Exercise Price	$ 38.90
Options exercisable at end of period Weighted Average Remaining Contractual Life	6.2
Options exercisable at end of period Aggregate Intrinsic Value	$ 6,842,000
Weighted average fair value of options granted during the period	$ 9.60