Concentration of Credit Risk - Summary of Funds Provided Ten Percent or More of Total Revenues (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Virtus Emerging Markets Opportunities Fund
Concentration Risk [Line Items]
Investment management, administration and shareholder service fees	$ 48,826	$ 49,085	$ 62,329
Virtus Multi-Sector Short Term Bond Fund
Concentration Risk [Line Items]
Investment management, administration and shareholder service fees	$ 44,577	$ 43,579	$ 49,174
Sales Revenue, Services, Net | Virtus Emerging Markets Opportunities Fund
Concentration Risk [Line Items]
Percent of total revenues	12.00%	15.00%	16.00%
Sales Revenue, Services, Net | Virtus Multi-Sector Short Term Bond Fund
Concentration Risk [Line Items]
Percent of total revenues	11.00%	14.00%	13.00%