Derivative Instruments And Hedging Activities - Narrative (Details) NOK in Millions, $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 NOK	Jun. 30, 2015 USD ($)	Sep. 30, 2013 USD ($)
Derivative [Line Items]
Unrealized losses related to foreign exchange contracts	$ 18.0
Loss in Accumulated OCI to be reclassified within twelve months		$ 4.7
Grand Canyon II [Member]
Derivative [Line Items]
Notional amount | NOK					NOK 434.1
Grand Canyon III [Member]
Derivative [Line Items]
Notional amount | NOK					NOK 185.2
Interest Rate Swaps [Member] | Former Term Loan Maturing June 2018 [Member]
Derivative [Line Items]
Notional amount							$ 148.1
Interest Rate Swaps [Member] | Nordea Q5000 Loan Maturing April 2020 [Member]
Derivative [Line Items]
Notional amount						$ 187.5
Other Income (Expense), Net [Member]
Derivative [Line Items]
Gains (losses) on hedge ineffectiveness		$ 0.0	$ 0.1	$ (5.1)