Significant Accounting Policies Accumulated Other Comprehensive Income (Loss), Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2016
Consolidated Legg Mason, Inc.
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax	$ (2,493)	$ 0	$ (2,493)	$ 0
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Loss on Derivative	$ (10,550)	$ (12,307)	(30,447)		$ (18,083)
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Loss on Derivative			$ (4,426)