Stock Based Compensation Plans, Stock options and restricted stock (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stock Based Compensation Plans [Abstract]
Number of shares available (in shares)	1,200,000
Exercise price as a percentage of fair market value of common stock on grant date, minimum (in hundredths)	100.00%
Life of options (in years)	10Y
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grants to officers and employees vesting period, minimum (in years)	1Y
Option grants to officers and employees vesting period, maximum (in years)	5Y
Stock-based compensation expense	$ 2,927,000	$ 3,251,000	$ 3,412,000
Intrinsic value of the options outstanding and fully vested	10,600,000	7,700,000	4,100,000
Cap on the appreciation of the market price over the exercise price	100,000,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,500,000	1,000,000	1,200,000
Stock-based compensation capitalized	200,000	200,000	200,000
Intrinsic value of options exercised	3,800,000	2,900,000	500,000
Unrecognized compensation cost	2,600,000
Unrecognized compensation cost, weighted average recognition period, minimum (in years)	2
Unrecognized compensation cost, weighted average recognition period, maximum (in years)	5
Average fair value of stock options granted (in dollars per share)	$ 17.98	$ 18.39	$ 5.24
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,200,000	1,200,000	1,200,000
Stock-based compensation capitalized	200,000	200,000	200,000
Unrecognized compensation cost	2,800,000
Series Z Incentive Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grants to officers and employees vesting period, minimum (in years)	8Y
Option grants to officers and employees vesting period, maximum (in years)	15Y
Stock-based compensation expense	1,500,000	2,300,000	1,500,000
Stock-based compensation capitalized	500,000	600,000	400,000
Intrinsic value of options exercised	17,300,000
Unrecognized compensation cost	$ 8,900,000
Unrecognized compensation cost, weighted average recognition period, maximum (in years)	15