Derivative Financial Instruments (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 26,725	$ 2,765	$ 38,510	$ 22,320
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	200,000		200,000
Other Contract [Member] | Other Nonoperating Income (Expense) [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 27,175	$ 4,432	$ 39,464	$ 26,836