Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated other comprehensive income, beginning balance	$ (211,336)	$ (153,457)
Other comprehensive (loss)/income before reclassifications	82,754	(72,726)
Amounts reclassified from accumulated other comprehensive income, net of tax	9,028	14,847
Other comprehensive income/(loss) attributable to G&W	91,782	(57,879)
Accumulated other comprehensive income, ending balance	(119,554)	(211,336)	$ (153,457)
Net income/(loss) attributable to noncontrolling interest	7,727	(41)	0
Foreign currency translation adjustment attributable to noncontrolling interest	17,836	8,805	0
Net unrealized loss on qualifying cash flow hedges, net of tax, attributable to noncontrolling interest	(540)	(256)	0
Comprehensive Income, Net of Tax, Attributable to Noncontrolling Interest	25,023	8,508	0
Tax benefit on qualifying cash flow hedges attributable to noncontrolling interest	232	110
Cumulative Foreign Currency Translation Adjustment [Member]
Accumulated other comprehensive income, beginning balance	(177,662)	(156,146)
Other comprehensive (loss)/income before reclassifications	89,025	(56,154)
Amounts reclassified from accumulated other comprehensive income, net of tax	0	34,638
Other comprehensive income/(loss) attributable to G&W	89,025	(21,516)
Accumulated other comprehensive income, ending balance	(88,637)	(177,662)	(156,146)
Tax benefit on foreign currency amount reclassified from AOCI		0
Defined Benefit Plans [Member]
Accumulated other comprehensive income, beginning balance	(19,948)	11,005
Other comprehensive (loss)/income before reclassifications	199	(31,155)
Amounts reclassified from accumulated other comprehensive income, net of tax	148	202
Other comprehensive income/(loss) attributable to G&W	347	(30,953)
Accumulated other comprehensive income, ending balance	(19,601)	(19,948)	11,005
Tax provision on benefit plans amount reclassified from AOCI	(83)	(113)
Net Unrealized Gain/(Loss) on Cash Flow Hedges [Member]
Accumulated other comprehensive income, beginning balance	(13,726)	(8,316)
Other comprehensive (loss)/income before reclassifications	(6,470)	14,583
Amounts reclassified from accumulated other comprehensive income, net of tax	8,880	(19,993)
Other comprehensive income/(loss) attributable to G&W	2,410	(5,410)
Accumulated other comprehensive income, ending balance	(11,316)	(13,726)	$ (8,316)
Tax (provision)/benefit on derivative amount reclassified from AOCI	$ (5,960)	$ 11,637