Derivatives Instruments (Notional Table) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | USD
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 0	$ 57,000
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | CAD
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	36,000	54,000
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | GBP
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	0	48,000
Designated as Hedging Instrument [Member] | Net Investment Hedging [Member] | CAD
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	575,000	900,000
Designated as Hedging Instrument [Member] | Net Investment Hedging [Member] | GBP
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	550,000	550,000
Not Designated as Hedging Instrument [Member] | USD
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	408,007	0
Not Designated as Hedging Instrument [Member] | CAD
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	80,000	37,000
Not Designated as Hedging Instrument [Member] | Net Investment Hedging [Member] | CAD
Derivatives, Fair Value [Line Items]
Notional Amount of Nonderivative Instruments	250,000	250,000
Not Designated as Hedging Instrument [Member] | Net Investment Hedging [Member] | GBP
Derivatives, Fair Value [Line Items]
Notional Amount of Nonderivative Instruments	$ 1,050,000	$ 1,050,000