Revenue Revenue by Asset Class (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Total Operating Revenues	$ 747,905	$ 793,842
Equity AUM [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	315,130	309,790
Fixed Income AUM [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	290,920	274,368
Alternative AUM [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	121,475	182,493
Liquidity AUM [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	$ 20,380	$ 27,191