Derivatives (Details 5) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Short-term Interest Rate Swap, 2005 | Not designated as hedging
Open interest rate contracts
Year Entered	2005
Year of Maturity	2016
Initial Notional Amount (in millions)	$ 4.0
Hedged Item	Interest rate component of an operating lease - not accounted for as a hedge
Interest Rate	5.20%
Short-term Interest Rate Cap, 2012 | Not designated as hedging
Open interest rate contracts
Year Entered	2012
Year of Maturity	2016
Initial Notional Amount (in millions)	$ 10.0
Hedged Item	Interest rate component of debt - not accounted for as a hedge
Interest Rate	1.50%
Short-term Interest Rate Swap, 2006 | Cash flow hedge | Designated as hedging instrument
Open interest rate contracts
Year Entered	2006
Year of Maturity	2016
Initial Notional Amount (in millions)	$ 14.0
Hedged Item	Interest rate component of debt - accounted for as cash flow hedge
Interest Rate	5.70%
Long-term Interest Rate Swap, 2012 | Not designated as hedging
Open interest rate contracts
Year Entered	2012
Year of Maturity	2023
Initial Notional Amount (in millions)	$ 23.0
Hedged Item	Interest rate component of debt - not accounted for as a hedge
Interest Rate	1.90%
Long-term Interest Rate Collar, 2013 | Cash flow hedge | Designated as hedging instrument
Open interest rate contracts
Year Entered	2013
Year of Maturity	2021
Initial Notional Amount (in millions)	$ 40.0
Hedged Item	Interest rate component of debt - not accounted for as a hedge
Long-term Interest Rate Collar, 2013 | Cash flow hedge | Designated as hedging instrument | Minimum
Open interest rate contracts
Interest Rate	2.90%
Long-term Interest Rate Collar, 2013 | Cash flow hedge | Designated as hedging instrument | Maximum
Open interest rate contracts
Interest Rate	4.80%