Goodwill and Other Intangible Assets - Schedule of Indefinite-lived Intangible Assets by Type (Details) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Indefinite-lived Intangible Assets | ||
| Indefinite-lived intangible assets, Beginning balance | $ 366,600 | $ 367,732 |
| Additions or transfers | 770,100 | (1,132) |
| Indefinite-lived intangible assets, Ending balance | 1,136,700 | 366,600 |
| Fund Advisory, Transfer Agent and Distribution Contracts [Member] | ||
| Indefinite-lived Intangible Assets | ||
| Indefinite-lived intangible assets, Beginning balance | 342,900 | 342,900 |
| Additions or transfers | 770,100 | |
| Indefinite-lived intangible assets, Ending balance | 1,113,000 | 342,900 |
| Trade Name | ||
| Indefinite-lived Intangible Assets | ||
| Indefinite-lived intangible assets, Beginning balance | 23,700 | 24,832 |
| Additions or transfers | (1,132) | |
| Indefinite-lived intangible assets, Ending balance | $ 23,700 | $ 23,700 |