Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated other comprehensive income/(loss), beginning balance	$ (105,534)	$ (197,316)
Other comprehensive income/(loss) before reclassifications	(38,261)	82,754
Amounts reclassified from accumulated other comprehensive income, net of tax	309	9,028
Other comprehensive income/(loss) attributable to G&W	(37,952)	91,782
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCI to Retained Earnings	0
Accumulated other comprehensive income/(loss), ending balance	(146,456)	(105,534)	$ (197,316)
Net income/(loss) attributable to noncontrolling interest	9,908	7,727	(41)
Foreign currency translation adjustment attributable to noncontrolling interest	(23,272)	17,836	8,805
Net unrealized loss on qualifying cash flow hedges, net of tax, attributable to noncontrolling interest	(361)	(540)	(256)
Comprehensive (loss)/income attributable to noncontrolling interest	(13,725)	25,023	8,508
Tax benefit on qualifying cash flow hedges attributable to noncontrolling interest	155	232	110
Cumulative Foreign Currency Translation Adjustment [Member]
Accumulated other comprehensive income/(loss), beginning balance	(74,617)	(163,642)
Other comprehensive income/(loss) before reclassifications	(69,886)	89,025
Amounts reclassified from accumulated other comprehensive income, net of tax	0	0
Other comprehensive income/(loss) attributable to G&W	(69,886)	89,025
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCI to Retained Earnings	0
Accumulated other comprehensive income/(loss), ending balance	(144,503)	(74,617)	(163,642)
Defined Benefit Plans [Member]
Accumulated other comprehensive income/(loss), beginning balance	(19,601)	(19,948)
Other comprehensive income/(loss) before reclassifications	30,690	199
Amounts reclassified from accumulated other comprehensive income, net of tax	163	148
Other comprehensive income/(loss) attributable to G&W	30,853	347
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCI to Retained Earnings	(132)
Accumulated other comprehensive income/(loss), ending balance	11,120	(19,601)	(19,948)
Tax (provision) on benefit plans amount reclassified from AOCI	(53)	(83)
Net Unrealized Gain/(Loss) on Cash Flow Hedges [Member]
Accumulated other comprehensive income/(loss), beginning balance	(11,316)	(13,726)
Other comprehensive income/(loss) before reclassifications	935	(6,470)
Amounts reclassified from accumulated other comprehensive income, net of tax	146	8,880
Other comprehensive income/(loss) attributable to G&W	1,081	2,410
United States Tax Cuts and Jobs Act 2017, Reclassification from AOCI to Retained Earnings	(2,838)
Accumulated other comprehensive income/(loss), ending balance	(13,073)	(11,316)	(13,726)
Tax (provision)/benefit on derivative amount reclassified from AOCI	(57)	(5,960)
AOCI Attributable to Parent [Member]
Other comprehensive income/(loss) attributable to G&W	(37,952)	$ 91,782	$ (92,517)
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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