Stock-Based Compensation Management Equity Plans (Details 10) - Management Equity Plan [Member] - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017	Mar. 31, 2016
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued		$ 70,026
Clarion Partners [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Profits interests equity plan participation percentage		15.00%
Deferred Compensation Arrangement with Individual, Allocated Share-based Compensation Expense			$ 15,200			$ 15,200
Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued		$ 16,200
Royce [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Profits interests equity plan participation percentage		19.00%
Stockholders' Equity Attributable to Noncontrolling Interest	[1]	$ 28,026	23,186		$ 28,026	23,186	$ 27,798	$ 22,202
Permal [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Aggregate Cost of Awards				$ 9,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Share-based Liabilities Paid				7,150
Deferred Compensation Arrangement with Individual, Compensation Expense				$ 3,481
ClearBridge Investments [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Profits interests equity plan participation percentage		15.00%
Aggregate Cost of Awards		$ 16,000			16,000
Deferred Compensation Arrangement with Individual, Allocated Share-based Compensation Expense		776	$ 817		$ 1,552	$ 1,635
Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued		$ 25,800

[1] (2) Related to Royce management equity plan.