Benefit Plans (Details Textual) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) plan	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Compensation and Retirement Disclosure [Abstract]
Employer discretionary contribution amount	$ 4.4	$ 3.8	$ 3.2
Number of non-contributory defined benefit pension plans | plan	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	$ 7.7
Long-term portion of the pension liability	28.3	25.6
AOCI net prior service cost	3.7
Future amortization of prior service cost	$ 0.3
Retirement age	65 years
Expense related to contributions	$ 0.1	0.1	$ 0.3
Total deferred compensation liability	16.2	13.8
Deferred compensation liability, current	$ 0.8	$ 1.2