Equity Compensation Plans (Details Textual) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012 Y	Mar. 31, 2011	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based Compensation Expense	$ 4,446	$ 3,818
Class A common stock reserved	6,955,761
Non vested stock option	6,071,378
Stock option expected to vest	5,326,199
Equity Compensation Plans (Textual) [Abstract]
Cash received from stock option exercised	14,589	3,579
Nonqualified stock option contractual term	10 years
Aggregate intrinsic value of stock option outstanding	486,392		445,510
Aggregate intrinsic value of stock option exercisable	351,903		337,647
Excess tax benefit from stock option exercised	29,705	1,383
Total unrecognized compensation cost related to nonvested share based compensation arrangements	33,028
Unrecognized compensation cost weighted average period	2.19
Total fair value of options vested	4,989	4,818
Grant date fair value restricted stock vested	305
Realized tax benefit from stock option exercised	$ 0	$ 0
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonqualified stock option, service vesting period	4 years
Non vested stock option	144,958
Stock option expected to vest	116,798
Key Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonqualified stock option, service vesting period	4 years
Key Employee [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonqualified stock option granted	229,009
Key Employee [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonqualified stock option granted	785,079