Employee Benefit Plans (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Benefit Plan Obligations (Textual) [Abstract]
Company's expense for its defined contribution plans	$ 8,800,000	$ 7,800,000	$ 5,300,000
Company contributed to the defined benefit pension plan to the next fiscal year	3,000,000
Contributions to the defined benefit pension plan	$ 3,000,000
Supplemental Employee Retirement Plan
Employee Benefit Plan Obligations (Textual) [Abstract]
Calculated rate for the supplemental employee retirement plan	2.10%	3.20%	4.20%
Discount rate	3.20%	4.20%	6.00%