Stock-Based Compensation Plans (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Shares
Exercised (in shares)	(116,517)
Granted (in shares)	113,804	144,827
Additional disclosures
Share-based compensation expense	$ 2,974,000	$ 2,834,000
Capitalized stock-based compensation cost	1,276,000	1,341,000
Stock Options
Additional disclosures
Unrecognized compensation cost for unvested stock options	4,356,000
Weighted average period for recognition of unrecognized compensation cost	2 years 5 months 1 day
Restricted stock
Additional disclosures
Outstanding unvested shares granted	394,868
Shares vested	126,169
Total fair value of shares vested	11,727,000	8,647,000
Unrecognized compensation cost for unvested restricted stock	$ 12,222,000
Weighted average period for recognition of unrecognized compensation cost	2 years 11 months 16 days
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)	$ 132.95
2009 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	247,403
Exercised (in shares)	(15,640)
Granted (in shares)	113,804
Forfeited (in shares)	(2,396)
Options outstanding at the end of the period (in shares)	343,171
Options exercisable at the end of the period (in shares)	102,243
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)	$ 95.80
Granted (in dollars per share)	$ 132.95
Forfeited (in dollars per share)	$ 99.69
Options outstanding at the end of the period (in dollars per share)	$ 109.98
Options exercisable at the end of the period (in dollars per share)	$ 92.48
Additional disclosures
Weighted average fair value per share (in dollars per share)	$ 29.05
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 (in years)	5 years
1994 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	1,112,959
Exercised (in shares)	(100,877)
Forfeited (in shares)	(1,135)
Options outstanding at the end of the period (in shares)	1,010,947
Options exercisable at the end of the period (in shares)	1,010,947
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)	$ 73.57
Forfeited (in dollars per share)	$ 48.60
Options outstanding at the end of the period (in dollars per share)	$ 96.20
Options exercisable at the end of the period (in dollars per share)	$ 96.20