Stock-Based Compensation Plans (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2013 item	Mar. 31, 2012
Additional disclosures
Stock-based compensation expense	$ 5,616,515	$ 2,974,000
Number of transitional awards maturing at the end of 2013 and 2014	2
Capitalized stock-based compensation cost	1,860,178	1,276,000
Stock Options
Additional disclosures
Unrecognized compensation cost for unvested stock options	6,632,039
Weighted average period for recognition of unrecognized compensation cost	2 years 6 months 7 days
Restricted stock
Weighted average assumptions
Percentage of granted award which will vest	33.00%
Award vesting period	3 years
Additional disclosures
Outstanding unvested shares granted	227,668
Shares vested	93,462
Total fair value of shares vested	8,981,349	11,727,000
Unrecognized compensation cost for unvested restricted stock	14,564,587
Weighted average period for recognition of unrecognized compensation cost	3 years 1 month 10 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)	$ 149.05
Restricted stock units
Weighted average assumptions
Dividend yield (as a percent)	2.80%
Percentage of granted award which will vest	33.00%
Award vesting period	3 years
Measurement period for total shareholder return of the Company's common stock	3 years
Percentage of stock based compensation elected to be received in the form of stock options upon the election of the recipient	25.00%
Additional disclosures
Stock-based compensation expense	15,349,000
Baseline share value (in dollars per share)	$ 130.23
Dividend yield (as a percent)	2.80%
Historical volatility (as a percent)	50.00%
Implied volatility (as a percent)	50.00%
Risk-free interest rate, minimum (as a percent)	0.08%
Risk-free interest rate, maximum (as a percent)	0.37%
Average estimated fair value (in dollars per share)	$ 110.00
Compensation expense related to the grants under the revised compensation framework	2,099,000
Capitalized stock-based compensation costs related to the grants under the revised compensation framework	$ 421,000
2009 Plan | Stock Options
Additional disclosures
Weighted average fair value per share (in dollars per share)	$ 26.78
Weighted average assumptions
Dividend yield (as a percent)	3.70%
Volatility (as a percent)	34.00%
Risk-free interest rate (as a percent)	0.91%
Expected life of option	5 years
Additional disclosures
Dividend yield (as a percent)	3.70%