Commitments and Contingencies - Additional Information (Detail) $ in Thousands			3 Months Ended		9 Months Ended
	Jun. 07, 2015 Plaintiff	Apr. 21, 2015 Plaintiff	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Loss Contingencies [Line Items]
Loss contingency, income tax benefit			$ (9,669)	$ 1,805	$ (28,360)	$ (24,311)
Virtus Investment Partners, Inc. Securities Litigation [Member]
Loss Contingencies [Line Items]
Number of plaintiffs | Plaintiff		3
Mark Youngers v. Virtus Investment Partners, Inc. et al [Member]
Loss Contingencies [Line Items]
Number of plaintiffs | Plaintiff	3
Unfavorable Regulatory Action [Member]
Loss Contingencies [Line Items]
Loss contingency, pre-tax					16,500
Loss contingency, income tax benefit					5,500
Loss contingency, net of tax benefit					$ 11,000