Share-Based Compensation (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011 Y	Dec. 31, 2010	Dec. 31, 2009
Share-Based Compensation (Textual) [Abstract]
Common stock shares available for future issuance	6,697,435
Number of shares available for issuance	2,646,923
Minimum vesting period of outstanding options and non vested shares	2 Years
Maximum vesting period of outstanding options and non vested shares	6 Years
Stock option granted	894,000	0	0
Aggregate intrinsic value of stock options exercised	$ 5,600,000	$ 3,300,000	$ 7,300,000
Actual tax benefit realized on options exercised	2,200,000	1,300,000	2,800,000
Total fair value of option vested	2,200,000	2,100,000	72,000
Weighted-average period of recognition of unrecognized compensation cost	1
Total unrecognized compensation cost related to stock options	4,200,000
Share based compensation arrangement by share based payment award equity instruments other than options non vested stock awards vest on second anniversary	25.00%
Share based compensation arrangement by share based payment award equity instruments other than options non vested stock awards vest on third anniversary	50.00%
Share based compensation arrangement by share based payment award equity instruments other than options non vested stock awards vest on fourth anniversary	25.00%
Shares of non-vested common stock granted	1,248
Estimated weighted average grant date fair value of stock options	$ 5.21
Shares of non-vested common stock to vest in equal installments	1,516	687
Maximum [Member]
Share-Based Compensation (Textual) [Abstract]
Expiration period of outstanding options	10 Years
Minimum [Member]
Share-Based Compensation (Textual) [Abstract]
Expiration period of outstanding options	5 Years
Board of Directors [Member]
Share-Based Compensation (Textual) [Abstract]
Period of equal annual installments for vesting of non-vested common stock	over 3 years from the date of grant
Number of restricted stock units granted	13,576
Employees - Non-Vested Shares 1 [Member]
Share-Based Compensation (Textual) [Abstract]
Period of equal annual installments for vesting of non-vested common stock	4 Years
Number of restricted stock units granted	1,234,470
Shares of non-vested common stock to vest in equal installments	1,157,470
Employees - Non-Vested Shares 2 [Member]
Share-Based Compensation (Textual) [Abstract]
Period of equal annual installments for vesting of non-vested common stock	6 Years
Shares of non-vested common stock to vest in equal installments	77,000
Employee Stock Option [Member]
Share-Based Compensation (Textual) [Abstract]
Compensation cost charged against income	1,600,000	2,600,000	1,900,000
Income tax benefit recognized during the period	600,000	1,000,000	800,000
Nonvested Stock Awards [Member]
Share-Based Compensation (Textual) [Abstract]
Weighted-average period of recognition of unrecognized compensation cost	3
Total unrecognized compensation cost related to stock options	22,400,000
Compensation cost charged against income	9,100,000	6,700,000	6,000,000
Income tax benefit recognized during the period	3,600,000	2,600,000	2,300,000
Restricted Stock Units (RSUs) [Member]
Share-Based Compensation (Textual) [Abstract]
Number of restricted stock units granted	0	0	84,757
Grant date fair value of restricted stock units	$ 22.90
Total value of restricted stock unit grant date fair value	$ 1,900,000