Employee Benefit Plans (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Benefit Plan Obligations (Textual) [Abstract]
Company's expense for its defined contribution plans	$ 11,200,000	$ 10,300,000	$ 8,800,000
Target asset allocation, fixed income investments, percentage	100.00%	49.00%
Amount of unamortized losses in other comprehensive income	64,600,000
Additional company contributions to settle pension obligation	10,300,000
Contributions to the defined benefit pension plan	$ 10,300,000
Supplemental Employee Retirement Plan
Employee Benefit Plan Obligations (Textual) [Abstract]
Calculated rate for the supplemental employee retirement plan	2.40%	2.90%	2.10%
Discount rate	2.90%	2.10%	3.20%