Stock-Based Compensation Plans (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Shares
Exercised (in shares)	(391,387)
Granted (in shares)	115,303	144,827
Additional disclosures
Stock-based compensation expense	$ 8,394,000	$ 7,614,000
Capitalized stock-based compensation cost	3,877,000	4,118,000
Stock Options
Additional disclosures
Unrecognized compensation cost for unvested stock options	2,730,000
Weighted average period for recognition of unrecognized compensation cost	1 year 11 months 1 day
Restricted stock
Additional disclosures
Outstanding unvested shares granted	203,308
Shares vested	317,685
Total fair value of shares vested	36,232,000	34,899,000
Weighted average period for recognition of unrecognized compensation cost	2 years 6 months
Unrecognized compensation cost for unvested restricted stock	$ 8,144,000
Restricted stock | Minimum
Additional disclosures
Grant date fair value per share (in dollars per share)	$ 48.60
Restricted stock | Maximum
Additional disclosures
Grant date fair value per share (in dollars per share)	$ 149.05
2009 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	247,403
Exercised (in shares)	(42,204)
Granted (in shares)	115,303
Forfeited (in shares)	(11,887)
Options outstanding at the end of the period (in shares)	308,615
Options exercisable at the end of the period (in shares)	75,679
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share)	$ 98.42
Exercised (in dollars per share)	$ 84.67
Granted (in dollars per share)	$ 133.16
Forfeited (in dollars per share)	$ 115.15
Options outstanding at the end of the period (in dollars per share)	$ 112.64
Options exercisable at the end of the period (in dollars per share)	$ 97.53
Additional disclosures
Weighted average fair value per share (in dollars per share)	$ 29.11
Weighted average assumptions
Dividend yield (as a percent)	3.50%
Volatility (as a percent)	35.00%
Risk-free interest rate (as a percent)	0.90%
Expected life of option	5 years
1994 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	1,112,959
Exercised (in shares)	(349,183)
Forfeited (in shares)	(6,779)
Options outstanding at the end of the period (in shares)	756,997
Options exercisable at the end of the period (in shares)	756,997
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share)	$ 94.10
Exercised (in dollars per share)	$ 68.28
Forfeited (in dollars per share)	$ 127.48
Options outstanding at the end of the period (in dollars per share)	$ 105.71
Options exercisable at the end of the period (in dollars per share)	$ 105.71