Activity of Hedging Instruments in Accumulated OCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	$ (170,478)
Unrealized gain (loss) on derivative instruments	1,183	$ 60
Realized losses reclassified into net income (loss)	(14)	232
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	(152,595)
Accumulated Net Gain (Loss) from Derivative and Nonderivative Instruments Designated as Hedging Instruments [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	(13,414)	(14,337)
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	$ (12,245)	$ (14,045)