Held for Sale and Discontinued Operations - Schedule of Financial Results for DMG's Discontinued Operations (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Valuation adjustment on disposal group					$ 316,840	$ 0	$ 0
Goodwill and other asset impairment charges					3,106	36,196	28,415
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest					(457,038)	(245,372)	(158,262)
DMG
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill and other asset impairment charges			$ 601,040	$ 50,619
DMG | Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net revenues					4,963,792	4,676,213	4,113,414
Expenses					4,962,686	4,634,782	3,994,624
Valuation adjustment on disposal group	$ 218,639	$ 98,201			316,840
Goodwill and other asset impairment charges	$ 41,537				41,537	651,659	253,000
Loss from discontinued operations before taxes					(357,271)	(610,228)	(134,210)
Income tax expense (benefit)					$ 99,768	$ (364,856)	$ 24,052