Revenues

The Company's revenues are recognized when a performance obligation is satisfied, which occurs when control of the services is transferred to customers. Investment management fees, distribution and service fees and administration and shareholder service fees are generally calculated as a percentage of average net assets of the investment portfolios managed. The net asset values from which investment management, distribution and service and administration and shareholder service fees are calculated are variable in nature and subject to factors outside of the Company's control such as deposits, withdrawals and market performance. Because of this, they are considered constrained until the end of the contractual measurement period (monthly or quarterly) which is when asset values are generally determinable.

Revenue Disaggregated by Source

The following table summarizes revenue by source:



	Three Months Ended March 31,
	2019		2018
($ in thousands)
Investment management fees
Open-end funds	$	53,293	$	54,361
Closed-end funds	10,019		10,378
Retail separate accounts	18,005		16,529
Institutional accounts	22,177		15,818
Structured products	1,647		2,326
Other products	777		1,064
Total investment management fees	105,918		100,476
Distribution and service fees	10,063		12,607
Administration and shareholder service fees	14,413		15,738
Other income and fees	324		207
Total revenues	$	130,718	$	129,028