Stockholders' Equity (Details Textual) (USD $)	1 Months Ended	12 Months Ended
	Jun. 30, 1999	Dec. 31, 2011 Y OptionPlan	Dec. 31, 2010 Y	Dec. 31, 2009 Y
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Share-based compensation expenses		$ 12,625,000	$ 10,256,000	$ 9,232,000
Shares available for future grant under stock compensation plans		2,349,146
Stockholders' Equity (Textual) [Abstract]
Number of stock option plans		3
Percentage of fair value of the common stock equal to exercise price		100.00%
Stock options exercisable terms, minimum		1
Stock options exercisable terms, maximum		5
Term of expiration of options granted		10 years
Percentage of payroll deductions		10.00%
Percentage of purchase price for stock acquired under the plan		85.00%
Number of shares issued under employee stock purchase plan		49,089	66,564	50,690
Purchase price of shares issued under employee stock purchase plan		$ 20.37	$ 14.29	$ 14.29
Share-based compensation (capitalized)		4,200,000	1,600,000	2,100,000
Shortfall in tax benefit		0	0	0
Net cash proceed from excise of stock options		1,200,000	2,100,000	300,000
Actual income tax benefit from excise of stock options		1,100,000	800,000	100,000
Shares available for future grant under stock compensation plans		2,349,146
Reduction in stock option shares granted		1
Reduction in shares available for future grant by restricted stock		1.44
Look back period to estimate expected volatility of stock option grants		5.5	5.5	5.5
Intrinsic value of outstanding stock option		6,400,000
Intrinsic value of exercisable stock option		4,200,000
Intrinsic value of exercised stock option		4,200,000
Remaining contract life of outstanding stock option		5.8
Remaining contract life of exercisable stock option		4.2
Number of Matured shares delivered in stock swap transactions		79,194	27,463	0
Criteria for ESOP		Within one year
Amount contributed to ESOP		200,000	200,000	200,000
Shares of common stock contributed to ESOP		6,729	5,108	8,347
Voluntary contributions by the eligible employees under the employee savings plan		amount equal to 100% of the first 2% of compensation and 75% of the next 4% of compensation based on the contributions made by the eligible employees
Employer contribution to employee saving plan First Criteria Percentage		100.00%
As employee savings plan employee contribution basis for employer contribution on first criteria percentage		2.00%
Employer contribution to employee saving plan Second Criteria Percentage		75.00%
As employee savings plan employee contribution basis for employer contribution on second criteria percentage		4.00%
Amount contributed to Employee savings plan		1,400,000	1,300,000	1,300,000
Shares of common stock contributed to the savings plan		44,258	31,960	50,988
Treasury Stock Value Acquired	13,300,000
Treasury stock acquired, shares	927,774	80,014	70,337	56,662
Average cost price per share of treasury shares purchased	$ 14.34
Treasury stock held, shares		484,471
Treasury Stock, Carrying Basis		12,400,000
Number of treasury shares used to fund the ESOP and 401k		763,083
Shareholder initial right agreement		10 years
Additional extended right agreement		10 years
Purchase of beneficial ownership		15% or more
General and Administrative Expense [Member]
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Share-based compensation expenses		11,900,000	9,300,000	8,400,000
Operating Lease Expense [Member]
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Share-based compensation expenses		300,000	300,000	400,000
Employee Stock Option [Member]
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Unrecognized compensation cost related to stock options		2,200,000
Weighted average recognition period of cost related to stock options		0.6
Shareholder Rights Plan [Member]
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Stock holders right to purchase a share		$ 0.0001
Purchase of preferred stock		250
Employee Stock Purchase Plan [Member]
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Shares available for future grant under stock compensation plans		49,754
Stockholders' Equity (Textual) [Abstract]
Shares available for future grant under stock compensation plans		49,754
Restricted Stock [Member]
Employee Service Share-based Compensation Allocation of Recognized Period Costs (Textual)
Unrecognized compensation cost related to stock options		15,700,000
Weighted average recognition period of cost related to stock options		1.0
Grant date fair value of shares vested		$ 8,700,000
Number of shares issued to employees, consultants and directors		499,050	388,650	433,210
Term of shares vested, Minimum		3 Year
Term of shares vested, Maximum		5 Year
Fair value of shares issued		$ 40	$ 25	$ 12