Subsequent Events - Additional Information (Detail)	Jan. 12, 2018 USD ($)	Jan. 04, 2018 USD ($) ft²	Dec. 01, 2017 USD ($)	Jan. 31, 2018 shares	Dec. 31, 2017 shares	Sep. 30, 2017 shares
Subsequent Event [Line Items]
Maximum common stock issuable under plan | shares					22,500,000	22,500,000
Manning and Napier Group LLC and Rainier Investment Management LLC [Member]
Subsequent Event [Line Items]
Business combination, agreement date			May 10, 2017
Business combination, cash paid			$ 1,000,000
Business acquisition, effective date of acquisition			Dec. 01, 2017
Business combination, assets acquired and liabilities assumed, assets			$ 122,000,000
Subsequent Event [Member] | Manning and Napier Group LLC and Rainier Investment Management LLC [Member]
Subsequent Event [Line Items]
Business combination, agreement date	May 10, 2017
Business combination, cash paid	$ 2,100,000
Business acquisition, effective date of acquisition	Jan. 12, 2018
Business combination, assets acquired and liabilities assumed, assets	$ 253,000,000
Subsequent Event [Member] | Sublease [Member] | Texas [Member]
Subsequent Event [Line Items]
Lease expiration date		Dec. 31, 2018
Operating sub-lease area | ft²		600
Term of lessee's operating lease renewal		1 year
Monthly rent expense for the initial term of the lease		$ 1,500
Subsequent Event [Member] | Dividend Reinvestment and Stock Purchase Plan [Member]
Subsequent Event [Line Items]
Maximum common stock issuable under plan | shares				1,550,000
Shares available for issuance under plan | shares				1,550,000