Long-Term Debt Reverse Treasury Rate Lock (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 23, 2014
Consolidated Legg Mason, Inc.
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax		$ (262)	$ 0	$ 233
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	$ 0	(368)	$ 0	405
Interest Rate Swap [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount					$ 250,000
Treasury Lock [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount					$ 650,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		$ (368)		$ 405