Acquisitions EnTrustPermal Restructuring (Details) - EnTrustPermal [Member] - USD ($) $ in Thousands		3 Months Ended			6 Months Ended	12 Months Ended		21 Months Ended
		Sep. 30, 2017	Mar. 31, 2016		Sep. 30, 2017	Mar. 31, 2017		Sep. 30, 2017	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Valuation Allowances and Reserves, Balance			$ 7,212			$ 9,069
Payments for Restructuring			24,035		$ 7,224	41,619
Restructuring Reserve		$ 4,466	17,527		4,466	9,874		$ 4,466	$ 0
Restructuring Reserve, Accrual Adjustment			41,562		1,816	33,966
Restructuring Reserve, Settled without Cash	[1]		1,734		2,104	7,819		11,657
Restructuring and Related Cost, Cost Incurred to Date		89,001			89,001			89,001
Restructuring and Related Cost, Incurred Cost		1,358			3,920
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Payments for Restructuring			21,938		4,560	29,211
Restructuring Reserve		142	9,643		142	3,323		142	0
Restructuring Reserve, Accrual Adjustment			31,581		1,379	22,891
Restructuring Reserve, Settled without Cash	[1]		591		2,100	4,423		7,114
Restructuring and Related Cost, Cost Incurred to Date		62,965			62,965			62,965
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Payments for Restructuring			2,097		2,664	12,408
Restructuring Reserve		4,324	7,884		4,324	6,551		4,324	$ 0
Restructuring Reserve, Accrual Adjustment			9,981	[2]	437	11,075	[2]
Restructuring Reserve, Settled without Cash	[1]		$ 1,143		4	$ 3,396		4,543
Restructuring and Related Cost, Cost Incurred to Date		26,036			26,036			26,036
Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost		2,000			2,000			2,000
Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost		$ 3,000			$ 3,000			$ 3,000

[1] (2) Includes stock-based compensation expense and accelerated fixed asset depreciation.

[2] (1) Includes lease loss reserve for space permanently abandoned of $9,069 for the year ended March 31, 2017, and $7,212 for the year ended March 31, 2016.