Stock-Based Compensation Plans (Details 3) (USD $)	12 Months Ended															12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Stock Options	Dec. 31, 2011 Stock Options	Dec. 31, 2010 Stock Options	Dec. 31, 2012 Restricted stock	Dec. 31, 2011 Restricted stock	Dec. 31, 2010 Restricted stock	Dec. 31, 2012 Restricted stock Minimum	Dec. 31, 2012 Restricted stock Maximum	Dec. 31, 2012 Non-Qualified Employee Stock Purchase Plan	Dec. 31, 2011 Non-Qualified Employee Stock Purchase Plan	Dec. 31, 2010 Non-Qualified Employee Stock Purchase Plan	Dec. 31, 1996 Non-Qualified Employee Stock Purchase Plan	Dec. 31, 2012 Non-Qualified Employee Stock Purchase Plan Full-time employees Minimum	Dec. 31, 2012 Non-Qualified Employee Stock Purchase Plan Other than full time employees	May 21, 2009 2009 Plan
Additional disclosures
Weighted average fair value per share (in dollars per share)				$ 29.11	$ 29.40	$ 19.45
Weighted average assumptions
Expected life of option				5 years	7 years	7 years
Dividend yield (as a percent)				3.50%	4.00%	5.50%
Volatility (as a percent)				35.00%	35.00%	43.00%
Risk-free interest rate (as a percent)				0.87%	3.04%	3.15%
Additional disclosures
Outstanding unvested shares granted							202,218	431,320
Restricted stock issued							96,592
Restricted stock vesting during period							$ 12,883,000
Shares vested							318,726
Grant date fair value per share (in dollars per share)										$ 48.60	$ 149.05
Total fair value of shares vested							36,337,000	35,029,000	9,805,000
Stock-based compensation expense	9,961,000	9,721,000	9,906,000									127,000	216,000	272,000
Capitalized stock-based compensation cost	5,140,000	5,284,000	5,117,000
Unrecognized compensation cost for unvested stock options				2,230,000
Unrecognized compensation cost for unvested restricted stock							6,705,000
Weighted average period for recognition of unrecognized compensation cost				1 year 8 months 23 days			2 years 3 months 29 days
Forfeiture rate (as a percent)				1.50%
Employee Stock Purchase Plan
Employee stock purchase plan, shares of common stock reserved for issuance															1,000,000
Employee stock purchase plan, remaining shares of common stock available for issuance												733,935						1,269,822
Employment period for applicability of Employee Stock Purchase Plan																1 month	12 months
Purchase period												7 months
Employee stock purchase plan, discounted stock price percentage												85.00%
Shares issued under employee stock purchase plan	6,260											6,260	6,972	8,137
Stock-based compensation expense	$ 9,961,000	$ 9,721,000	$ 9,906,000									$ 127,000	$ 216,000	$ 272,000