Fair Value Measurements - Summary of the assets and liabilities that are measured at fair value on a recurring basis (Details) - USD ($) | 3 Months Ended | 12 Months Ended |
Mar. 31, 2022 | Mar. 31, 2021 | Dec. 31, 2021 |
Asset of BSIF and consolidated Funds | | | |
Total fair value assets | $ 53,400,000 | | $ 54,500,000 |
Transfers between levels two or three | 0 | $ 0 | |
Investments in unconsolidated funds | | | |
Asset of BSIF and consolidated Funds | | | |
Uncategorized | $ 4,500,000 | | 4,900,000 |
Real estate investment funds | Minimum | | | |
Asset of BSIF and consolidated Funds | | | |
Term over which the underlying assets are expected to be liquidated by the investees | 1 year | | |
Consolidated Entity Excluding Consolidated Funds | | | |
Asset of BSIF and consolidated Funds | | | |
Uncategorized | $ 4,500,000 | | |
Consolidated Entity Excluding Consolidated Funds | Investments in separate accounts | | | |
Asset of BSIF and consolidated Funds | | | |
Investments in separate accounts | 4,500,000 | | 4,600,000 |
Consolidated Entity Excluding Consolidated Funds | Investments related to long-term incentive compensation plans | | | |
Asset of BSIF and consolidated Funds | | | |
Investments related to long-term incentive compensation plans | 44,400,000 | | 45,000,000 |
Investments in unconsolidated Funds | 44,400,000 | | 45,000,000 |
Consolidated Entity Excluding Consolidated Funds | Investments in unconsolidated funds | | | |
Asset of BSIF and consolidated Funds | | | |
Uncategorized | 4,500,000 | | 4,900,000 |
Investments in unconsolidated Funds | 4,500,000 | | 4,900,000 |
Consolidated Entity Excluding Consolidated Funds | Investment Funds Subject to Longer Redemption Restrictions | | | |
Asset of BSIF and consolidated Funds | | | |
Uncategorized | 4,400,000 | | 4,800,000 |
Quoted prices in active markets (Level I) | | | |
Asset of BSIF and consolidated Funds | | | |
Total fair value assets | $ 48,900,000 | | $ 49,600,000 |
Quoted prices in active markets (Level I) | Consolidated Entity Excluding Consolidated Funds | | | |
Asset of BSIF and consolidated Funds | | | |
Investment in equity securities | 100.00% | | 100.00% |
Quoted prices in active markets (Level I) | Consolidated Entity Excluding Consolidated Funds | Investments in separate accounts | | | |
Asset of BSIF and consolidated Funds | | | |
Investments in separate accounts | $ 4,500,000 | | $ 4,600,000 |
Quoted prices in active markets (Level I) | Consolidated Entity Excluding Consolidated Funds | Investments related to long-term incentive compensation plans | | | |
Asset of BSIF and consolidated Funds | | | |
Investments related to long-term incentive compensation plans | 44,400,000 | | 45,000,000 |
Quoted prices in active markets (Level I) | Consolidated Entity Excluding Consolidated Funds | Investments in unconsolidated funds | | | |
Asset of BSIF and consolidated Funds | | | |
Investments in unconsolidated Funds | 0 | | 0 |
Significant other observable inputs (Level II) | | | |
Asset of BSIF and consolidated Funds | | | |
Total fair value assets | 0 | | 0 |
Significant other observable inputs (Level II) | Consolidated Entity Excluding Consolidated Funds | Investments in separate accounts | | | |
Asset of BSIF and consolidated Funds | | | |
Investments in separate accounts | 0 | | 0 |
Significant other observable inputs (Level II) | Consolidated Entity Excluding Consolidated Funds | Investments related to long-term incentive compensation plans | | | |
Asset of BSIF and consolidated Funds | | | |
Investments related to long-term incentive compensation plans | 0 | | 0 |
Significant other observable inputs (Level II) | Consolidated Entity Excluding Consolidated Funds | Investments in unconsolidated funds | | | |
Asset of BSIF and consolidated Funds | | | |
Investments in unconsolidated Funds | 0 | | 0 |
Significant unobservable inputs (Level III) | | | |
Asset of BSIF and consolidated Funds | | | |
Total fair value assets | 0 | | 0 |
Significant unobservable inputs (Level III) | Consolidated Entity Excluding Consolidated Funds | Investments in separate accounts | | | |
Asset of BSIF and consolidated Funds | | | |
Investments in separate accounts | 0 | | 0 |
Significant unobservable inputs (Level III) | Consolidated Entity Excluding Consolidated Funds | Investments related to long-term incentive compensation plans | | | |
Asset of BSIF and consolidated Funds | | | |
Investments related to long-term incentive compensation plans | 0 | | 0 |
Significant unobservable inputs (Level III) | Consolidated Entity Excluding Consolidated Funds | Investments in unconsolidated funds | | | |
Asset of BSIF and consolidated Funds | | | |
Investments in unconsolidated Funds | $ 0 | | $ 0 |