Held for Sale and Discontinued Operations Financial results for discontinued operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill and other asset impairment charges	$ 0	$ 124,892	$ 3,106
Valuation adjustment on disposal group	0	0	316,840
Loss on sale of discontinued operations before taxes	(24,248)	(23,022)
Net (loss) income from discontinued operations, net of tax	(9,653)	105,483	(457,038)
DMG - discontinued operations | Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net revenues	0	2,713,059	4,963,792
Expenses	0	2,543,865	4,962,686
Goodwill and other asset impairment charges	0	0	41,537
Valuation adjustment on disposal group	0	0	316,840
Income (loss) from discontinued operations before taxes	0	169,194	(357,271)
Loss on sale of discontinued operations before taxes	(7,996)	(23,022)	0
Income tax expense	$ 1,657	$ 40,689	$ 99,768