Derivatives and Hedging Derivative Instruments and Hedging Activities Disclosure (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Mar. 31, 2018	Oct. 10, 2017	Sep. 30, 2017	Jul. 26, 2017	Jun. 06, 2017	Mar. 31, 2017
Derivative
Derivative, Term of Contract	4 years 245 days
Other Assets [Member]
Derivative
Amount Net for Fair Value of Derivative Assets and (Liabilities)		$ 4,904					$ 2,718
Other Liabilities [Member]
Derivative
Amount Net for Fair Value of Derivative Assets and (Liabilities)		6,446					$ 4,522
Foreign Exchange Forward [Member]
Derivative
Derivative, Notional Amount		285,665
Derivative, Average Remaining Maturity	4 months
Future [Member]
Derivative
Derivative, Notional Amount		140,375
Derivative, Average Remaining Maturity	3 months
Total Return Swap [Member]
Derivative
Derivative, Notional Amount		50,071		$ 48,639
Aggregate Counterparty Investment in ETF		48,639
Derivative Financial Instruments, Assets [Member] | Future [Member]
Derivative
Derivative, Notional Amount				$ 49,175
Total Return Swap Expiring in October 2018 [Member]
Derivative
Derivative, Notional Amount		$ 6,064
Derivative, Fixed Interest Rate		1.60%
Total Return Swap Expiring in October 2018 [Member] | Total Return Swap [Member]
Derivative
Aggregate Counterparty Investment in ETF			$ 5,290
Total Return Swap Expiring in July 2018 [Member]
Derivative
Derivative, Fixed Interest Rate		1.60%
Total Return Swap Expiring in July 2018 [Member] | Total Return Swap [Member]
Derivative
Aggregate Counterparty Investment in ETF					$ 23,096
Legg Mason Global Infrastructure ETF [Member]
Derivative
Derivative, Notional Amount		$ 22,156
ClearBridge All Cap Growth ETF [Member]
Derivative
Derivative, Fixed Interest Rate		1.35%
ClearBridge All Cap Growth ETF [Member] | Total Return Swap [Member]
Derivative
Aggregate Counterparty Investment in ETF						$ 20,253
ClearBridge All Cap Growth ETF [Member] | Total Return Swap [Member]
Derivative
Derivative, Notional Amount		$ 21,851