Accumulated Other Comprehensive Income/(Loss) AOCI Attributable to G&W (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, beginning balance	$ (105,534)	$ (197,316)
Other comprehensive income/(loss) before reclassifications	(26,962)	46,771
Amounts reclassified from accumulated other comprehensive loss, net of tax (provision)/benefit	(204)	5,105
Current period change in OCI	(27,166)	51,876
Accumulated other comprehensive income loss, ending balance	(135,670)	(145,440)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, beginning balance	(74,617)	(163,642)
Other comprehensive income/(loss) before reclassifications	(36,698)	53,482
Amounts reclassified from accumulated other comprehensive loss, net of tax (provision)/benefit	0	0
Current period change in OCI	(36,698)	53,482
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCI to Retained Earnings	0
Accumulated other comprehensive income loss, ending balance	(111,315)	(110,160)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, beginning balance	(19,601)	(19,948)
Other comprehensive income/(loss) before reclassifications	0	(2,263)
Amounts reclassified from accumulated other comprehensive loss, net of tax (provision)/benefit	86	76
Current period change in OCI	86	(2,187)
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCI to Retained Earnings	(132)
Accumulated other comprehensive income loss, ending balance	(19,647)	(22,135)
Tax (provision) on amounts reclassified from AOCI for defined benefit plans	(28)	(40)
Net Unrealized Gain/(Loss) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, beginning balance	(11,316)	(13,726)
Other comprehensive income/(loss) before reclassifications	9,736	(4,448)
Amounts reclassified from accumulated other comprehensive loss, net of tax (provision)/benefit	(290)	5,029
Current period change in OCI	9,446	581
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCI to Retained Earnings	(2,838)
Accumulated other comprehensive income loss, ending balance	(4,708)	(13,145)
Tax (provision)/benefit on amounts reclassified from AOCI for cash flow hedges	115	$ (3,381)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCI to Retained Earnings	$ (2,970)

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

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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