Consolidated Sponsored Investment Products - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	$ 62,086	$ 139,054
Debt Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	52,925	47,114
Equity Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	9,161	91,940
Level 1 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	9,161	91,940
Level 1 [Member] | Debt Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	0
Level 1 [Member] | Equity Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	9,161	91,940
Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	52,925	47,114
Level 2 [Member] | Debt Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	52,925	47,114
Level 2 [Member] | Equity Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	0
Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	0
Level 3 [Member] | Debt Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	0
Level 3 [Member] | Equity Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investments of Consolidated Sponsored Investment Products at Fair Value	$ 0