Stock-Based Compensation (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Stock-Based Compensation [Abstract]
Stock-based compensation costs - expense	$ 2,844,000	$ 2,450,000
Stock-based compensation costs - capitalized	2,864,000	1,910,000
Unrecognized compensation cost related to unvested stock option and restricted stock grants	$ 48,300,000
Weighted average period over which cost is recognized, years	2.7
Stock options, outstanding at December 31, 2011 number of options	4,741,732
Stock options, granted, number of options	5,300
Stock options, exercised, number of options	(189,475)
Stock options, forfeited or expired, number of options	(16,976)
Stock options, outstanding at March 31, number of options	4,540,581
Stock options, exercisable at December 31, 2011	3,322,436
Stock options, outstanding at December 31, 2011 weighted average exercise price	$ 21.24
Stock options, granted, weighted average exercise price	$ 32.27
Stock options, exercised, weighted average exercise price	$ 13.41
Stock options, forfeited or expired, weighted average exercise price	$ 37.74
Stock options, outstanding at March 31, weighted average exercise price	$ 21.52
Stock options exercisable at March 31, weighted average exercise price	$ 15.84
Restricted Stock, Unvested shares at December 31, 2011 Number of Shares	1,019,737
Restricted Stock, Granted, Number of Shares	4,689
Restricted Stock, Vested, Number of Shares	(14,868)
Restricted Stock, Forfeited, Number of Shares	(22,745)
Restricted Stock, Unvested shares at March 31, Number of Shares	986,813
Restricted Stock, Unvested shares at December 31, 2011 Weighted Average Grant Date Fair Value	$ 36.71
Restricted Stock, Vested, Weighted Average Grant Date Fair Value	$ 36.72
Restricted Stock, Granted, Weighted Average Grant Date Fair Value	$ 32.35
Restricted Stock, Forfeited, Weighted Average Grant Date Fair Value	$ 37.46
Restricted Stock, Unvested shares at March 31, Weighted Average Grant Date Fair Value	$ 36.70