Long-term debt (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Amount of debt issuance costs in other assets, netted against long term debt [Member]
Long-Term Debt [Line Items]
Debt issuance costs	$ 4.9
Amount of debt issuance costs in prepaid and other current assets, netted against long term debt [Member]
Long-Term Debt [Line Items]
Debt issuance costs	$ 1.2