Derivative Financial Instruments (Amounts Included in AOCL) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Derivative Gains Included in Accumulated Other Comprehensive Loss [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	$ (34,776)		$ (30,126)	$ (16,587)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	(1,937)	[1]	(6,699)	(14,904)
Reclassification of net loss (gain) on cash flow hedges to income(1)	2,958	[1]	2,049	1,365
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	$ (33,755)		$ (34,776)	$ (30,126)

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