Share-Based Compensation (Details Textual) (USD $)	3 Months Ended
	Mar. 31, 2012 Y	Mar. 31, 2011 Y
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Share-based compensation expenses	$ 3,629,000	$ 2,684,000
Stockholders' Equity (Textual) [Abstract]
Share-based compensation (capitalized)	1,300,000	1,000,000
Net cash proceed from excise of stock options	300,000	700,000
Actual income tax benefit from excise of stock options	100,000	900,000
Look back period to estimate expected volatility of stock option grants	5.5	5.5
Intrinsic value of outstanding stock option	5,700,000
Intrinsic value of exercisable stock option	5,400,000
Intrinsic value of exercised stock option	400,000
Remaining contract life of outstanding stock option	6.5
Remaining contract life of exercisable stock option	5.0
General and Administrative Expense [Member]
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Share-based compensation expenses	3,400,000	2,500,000
Operating Lease Expense [Member]
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Share-based compensation expenses	100,000	100,000
Employee Stock Option [Member]
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Unrecognized compensation cost related to options	6,100,000
Weighted average recognition period of cost related to options	1.5
Restricted Stock [Member]
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Unrecognized compensation cost related to options	27,300,000
Weighted average recognition period of cost related to options	1.5
Grant date fair value of shares vested	$ 8,300,000