Stock-Based Compensation (Details Textual) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Number of common stock shares which are authorized to issue awards	24.3
Common Stock, Capital Shares Reserved for Future Issuance	20.5
Shares available for future issuance	3.8
Payout Percentage	100.00%
Undistributed performance share units	0.4
Weighted-average grant date fair value of undistributed performance share units	$ 68.27
Undistributed and vested performance share units	0.4
Maximum [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Potential increase for payout percentage	200.00%
Performance Shares [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Award service period	3 years
Payout Percentage	153.20%	86.90%	52.50%
Total unrecognized compensation cost	$ 15.9
Weighted average period of recognition	2 years 2 months 24 days
Estimated forfeiture rate	16.50%
Restricted Stock Units (RSUs) [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Award service period	3 years
Total unrecognized compensation cost	14.9
Weighted average period of recognition	2 years 4 months 18 days
Estimated forfeiture rate	16.90%
Stock Appreciation Rights [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Award expiration period	7 years
Vesting percentage	33.33%
Total unrecognized compensation cost	$ 8.5
Weighted average period of recognition	2 years 3 months 24 days
Estimated forfeiture rate	15.60%