Intangible Assets and Goodwill Indefinite Lived Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2016
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets (Excluding Goodwill)								$ 3,260,317	$ 3,638,739
Other Fund Management Contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets (Excluding Goodwill)								473,360	557,305
Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets (Excluding Goodwill)								48,602	68,479
EnTrust Global [Member]
Indefinite-lived Intangible Assets [Line Items]
Other Indefinite-lived Intangible Assets	$ 401,404				$ 401,404
Indefinite-Lived Trade Names	28,500				28,500
EnTrust Global [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Impairment of Intangible Assets	18,200
EnTrust Global [Member] | Fund management contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Impairment of Intangible Assets	274,600	$ 195,000
Indefinite-lived Intangible Assets (Excluding Goodwill)								$ 126,804	$ 401,404
RARE Infrastructure, Ltd [Member]
Indefinite-lived Intangible Assets [Line Items]
Other Indefinite-lived Intangible Assets	120,800				120,800
Indefinite-Lived Trade Names	2,800			$ 3,057	$ 2,800
RARE Infrastructure, Ltd [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Impairment of Intangible Assets	1,000			$ 2,000
RARE Infrastructure, Ltd [Member] | Fund management contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Impairment of Intangible Assets	$ 65,000
Permal [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Impairment of Intangible Assets							$ 17,000
Indefinite-lived Intangible Assets (Excluding Goodwill)										$ 21,100
Permal [Member] | Royalty [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input							1.50%
Permal [Member] | Measurement Input, Discount Rate [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input										16.00%
Permal [Member] | Cash Flow Growth Rate [Member] | Minimum [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input										3.00%
Permal [Member] | Cash Flow Growth Rate [Member] | Maximum [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input										9.00%
Permal [Member] | Cash Flow Growth Rate [Member] | Weighted Average [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input										7.00%
RARE Infrastructure, Ltd [Member] | Royalty [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	1.00%			1.00%	1.00%
RARE Infrastructure, Ltd [Member] | Measurement Input, Discount Rate [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input				16.50%				16.50%
RARE Infrastructure, Ltd [Member] | Measurement Input, Discount Rate [Member] | Fund management contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	16.50%				16.50%
RARE Infrastructure, Ltd [Member] | Cash Flow Growth Rate [Member] | Minimum [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	1.00%			5.00%	1.00%
RARE Infrastructure, Ltd [Member] | Cash Flow Growth Rate [Member] | Minimum [Member] | Fund management contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	4.00%				4.00%
RARE Infrastructure, Ltd [Member] | Cash Flow Growth Rate [Member] | Maximum [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	5.00%			18.00%	5.00%
RARE Infrastructure, Ltd [Member] | Cash Flow Growth Rate [Member] | Maximum [Member] | Fund management contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	5.00%				5.00%
RARE Infrastructure, Ltd [Member] | Cash Flow Growth Rate [Member] | Weighted Average [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	4.00%			8.00%	4.00%
RARE Infrastructure, Ltd [Member] | Cash Flow Growth Rate [Member] | Weighted Average [Member] | Fund management contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	5.00%				5.00%
EnTrust Global [Member] | Royalty [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	1.00%				1.00%
EnTrust Global [Member] | Measurement Input, Discount Rate [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	16.50%				16.50%
EnTrust Global [Member] | Measurement Input, Discount Rate [Member] | Fund management contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	17.00%	15.00%			17.00%	15.00%
EnTrust Global [Member] | Cash Flow Growth Rate [Member] | Minimum [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	0.00%				0.00%
EnTrust Global [Member] | Cash Flow Growth Rate [Member] | Minimum [Member] | Fund management contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	(19.00%)	(13.00%)			(19.00%)	(13.00%)
EnTrust Global [Member] | Cash Flow Growth Rate [Member] | Maximum [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	5.00%				5.00%
EnTrust Global [Member] | Cash Flow Growth Rate [Member] | Maximum [Member] | Fund management contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	4.00%	6.00%			4.00%	6.00%
EnTrust Global [Member] | Cash Flow Growth Rate [Member] | Weighted Average [Member] | Trade Names
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	4.00%				4.00%
EnTrust Global [Member] | Cash Flow Growth Rate [Member] | Weighted Average [Member] | Fund management contracts [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Measurement Input	3.00%	5.00%			3.00%	5.00%
Customer Contracts [Member] | RARE Infrastructure, Ltd [Member]
Indefinite-lived Intangible Assets [Line Items]
Impairment of Intangible Assets			$ 32,000		$ 6,400	$ 18,000