Accumulated Other Comprehensive Income/(Loss) AOCI Attributable to G&W (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income/(loss), beginning balance	$ (105,534)	$ (197,316)
Other comprehensive income/(loss) before reclassifications	(26,469)	72,147
Amounts reclassified from accumulated other comprehensive loss, net of tax (provision)/benefit	(103)	8,050
Current period change in OCI	(26,572)	80,197
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCL to Retained Earnings	0
Accumulated other comprehensive income/(loss), ending balance	(135,076)	(117,119)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income/(loss), beginning balance	(74,617)	(163,642)
Other comprehensive income/(loss) before reclassifications	(41,395)	81,412
Amounts reclassified from accumulated other comprehensive loss, net of tax (provision)/benefit	0	0
Current period change in OCI	(41,395)	81,412
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCL to Retained Earnings	0
Accumulated other comprehensive income/(loss), ending balance	(116,012)	(82,230)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income/(loss), beginning balance	(19,601)	(19,948)
Other comprehensive income/(loss) before reclassifications	0	(2,262)
Amounts reclassified from accumulated other comprehensive loss, net of tax (provision)/benefit	129	113
Current period change in OCI	129	(2,149)
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCL to Retained Earnings	(132)
Accumulated other comprehensive income/(loss), ending balance	(19,604)	(22,097)
Tax (provision) on amounts reclassified from AOCL for defined benefit plans	(42)	(60)
Net Unrealized Gain/(Loss) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income/(loss), beginning balance	(11,316)	(13,726)
Other comprehensive income/(loss) before reclassifications	14,926	(7,003)
Amounts reclassified from accumulated other comprehensive loss, net of tax (provision)/benefit	(232)	7,937
Current period change in OCI	14,694	934
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCL to Retained Earnings	(2,838)
Accumulated other comprehensive income/(loss), ending balance	540	(12,792)
Tax (provision)/benefit on amounts reclassified from AOCL for cash flow hedges	76	(5,347)
AOCL Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Current period change in OCI	(26,572)	$ 80,197
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCL to Retained Earnings	$ (2,970)

United States Tax Cuts and Jobs Act 2017, Reclassification from AOCI to Retained Earnings

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