Benefit Plans (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 noncontributory_defined_benefit_pension_plans	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Employer discretionary contribution amount	$ 3.2	$ 3.4	$ 4.1
Number of non-contributory defined benefit pension plans	2
Period of average compensation for pension benefit computation	5 years
Age limit for a lump sum payment	55 years
Deferred compensation arrangement with Individual, recorded liability	7.1
Long-term portion of the pension liability	24.9	19.8
AOCI net prior service cost	4.2
Future amortization of prior service cost	0.4
Retirement age	65 years
Expense related to contributions	0.3	0.2	0.4
Total deferred compensation liability	11.0	9.8
Deferred compensation liability, current	$ 0.9	$ 0.3