Consolidated Statements of Changes in Equity Statement - USD ($) $ in Thousands	Total	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]	Class A Common Stock [Member] Common Stock [Member]	Class B Common Stock [Member] Common Stock [Member]	Conversion of Class B Common Stock to Class A Common Stock [Member]	Conversion of Class B Common Stock to Class A Common Stock [Member] Class A Common Stock [Member] Common Stock [Member]	Conversion of Class B Common Stock to Class A Common Stock [Member] Class B Common Stock [Member] Common Stock [Member]	Settlement of the prepaid stock purchase contract component of the TEUs [Member]	Settlement of the prepaid stock purchase contract component of the TEUs [Member] Additional Paid-in Capital [Member]	Settlement of the prepaid stock purchase contract component of the TEUs [Member] Class A Common Stock [Member] Common Stock [Member]
Stockholders' equity, balance at Dec. 31, 2013	$ 2,149,070	$ 1,302,521	$ 1,058,884	$ 6,089	$ (220,361)	$ 1,275	$ 646	$ 16
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income/(loss) attributable to G&W	260,755		260,755
Net (loss)/income attributable to noncontrolling interest	251					251
Net income/(loss) including portion attributable to noncontrolling interest	261,006
Other comprehensive income/loss including portion attributable to noncontrolling interest	(78,341)			(78,341)
Conversion of shares to Class A common stock									$ 0	$ 6	$ 6
Value of stock issued for stock-based compensation	11,819	11,815					4
Compensation cost related to stock-based compensation	12,819	12,819
Cash distribution to noncontrolling interest	(405)					(405)
Excess income tax benefits from stock-based compensation	6,198	6,198
Value of treasury stock repurchased	(4,186)				(4,186)
Stockholders' equity, balance at Dec. 31, 2014	2,357,980	1,333,353	1,319,639	(72,252)	(224,547)	1,121	656	10
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income/(loss) attributable to G&W	225,037		225,037
Net (loss)/income attributable to noncontrolling interest	0
Net income/(loss) including portion attributable to noncontrolling interest	225,037
Other comprehensive income/loss including portion attributable to noncontrolling interest	(81,205)			(81,205)
Conversion of shares to Class A common stock									0	2	2	$ 0	$ 36	$ 36
Value of stock issued for stock-based compensation	6,829	6,826					3
Compensation cost related to stock-based compensation	14,421	14,421
Excess income tax benefits from stock-based compensation	1,432	1,432
Purchase of noncontrolling interest	(2,582)	(1,461)				(1,121)
Value of treasury stock repurchased	(3,261)				(3,261)
Stockholders' Equity, Other	(810)	(810)
Stockholders' equity, balance at Dec. 31, 2015	2,519,461	1,355,345	1,544,676	(153,457)	(227,808)	0	697	8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income/(loss) attributable to G&W	141,137		141,137
Net (loss)/income attributable to noncontrolling interest	(41)					(41)
Net income/(loss) including portion attributable to noncontrolling interest	141,096
Other comprehensive income/(loss) attributable to G&W	(57,879)			(92,517)
Other comprehensive income/(loss) attributable to noncontrolling interest						8,549
Other comprehensive income/loss including portion attributable to noncontrolling interest	(83,968)
Value of stock issued - equity offering	285,756	285,716					40
Conversion of shares to Class A common stock									$ 0	$ 0	$ 0
Value of stock issued for stock-based compensation	8,294	8,289					5
Compensation cost related to stock-based compensation	18,884	18,884
Income tax deficiencies from stock-based compensation	(281)	(281)
Value of treasury stock repurchased	(4,540)				(4,540)
Settlement of deferred stock awards	2,069	2,069
Issuance of noncontrolling interest	300,342	(18,327)				284,031
Stockholders' Equity, Other	8	8
Stockholders' equity, balance at Dec. 31, 2016	$ 3,187,121	$ 1,651,703	$ 1,685,813	$ (211,336)	$ (232,348)	$ 292,539	$ 742	$ 8