Classification within AOCL on the Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Foreign currency translation	$ 1,511	$ 1,448
Derivative instruments designated as cash flow hedges	(11,521)	(11,633)
Postretirement medical plans	251	251
Accumulated other comprehensive loss	$ (9,759)	$ (9,934)

Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant