Subsequent Events	12 Months Ended
Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Securities Purchase Agreement On February 1, 2018, the Company entered into an agreement to acquire (the "Purchase Agreement" or the "Transaction") a majority interest in Sustainable Growth Advisers, LP ("SGA"), an investment manager specializing in U.S. and global growth equity portfolios. The purchase price payable by the Company at the Closing is $129.5 million, subject to certain potential adjustments. The transaction is expected to close in mid-2018, subject to customary closing conditions and client approvals. The Purchase Agreement contains customary termination rights for the Company and SGA, including in the event the Transaction is not consummated on or before September 30, 2018 (the “Termination Date”). The Purchase Agreement also contains customary representations, warranties, covenants and indemnification and escrow provisions. Credit Agreement On February 15, 2018, the Company amended its Credit Agreement that resulted in $105.0 million of additional Term Loan commitments to fund its proposed acquisition of SGA. The $105.0 million will be drawn at the closing of the SGA acquisition and is subject to a delayed draw fee. The amended Credit Agreement removed the financial maintenance covenant on the Term Loan and replaced the existing financial maintenance covenant on the $100.0 million Credit Facility with a net leverage ratio covenant, defined as net debt divided by EBITDA, set at 2.5 to 1, that is in place when $30.0 million or more has been drawn down on the revolving credit facility. In addition, the applicable margin in the case of LIBOR-based loans was reduced by 1.25% to 2.50% and will range from 2.25% to 2.50% based on the secured net leverage ratio of the Company. Dividends Declared On February 14, 2018, the Company declared a quarterly cash dividend of $0.45 per common share to be paid on May 15, 2018 to shareholders of record at the close of business on April 30, 2018. The Company also declared a quarterly cash dividend of $1.8125 per share on the Company's 7.25% mandatory convertible preferred stock to be paid on May 1, 2018 to shareholders of record at the close of business on April 16, 2018.

Subsequent Events

Securities Purchase Agreement

On February 1, 2018, the Company entered into an agreement to acquire (the "Purchase Agreement" or the "Transaction") a majority interest in Sustainable Growth Advisers, LP ("SGA"), an investment manager specializing in U.S. and global growth equity portfolios. The purchase price payable by the Company at the Closing is $129.5 million, subject to certain potential adjustments. The transaction is expected to close in mid-2018, subject to customary closing conditions and client approvals. The Purchase Agreement contains customary termination rights for the Company and SGA, including in the event the Transaction is not consummated on or before September 30, 2018 (the “Termination Date”). The Purchase Agreement also contains customary representations, warranties, covenants and indemnification and escrow provisions.

Credit Agreement

On February 15, 2018, the Company amended its Credit Agreement that resulted in $105.0 million of additional Term Loan commitments to fund its proposed acquisition of SGA. The $105.0 million will be drawn at the closing of the SGA acquisition and is subject to a delayed draw fee. The amended Credit Agreement removed the financial maintenance covenant on the Term Loan and replaced the existing financial maintenance covenant on the $100.0 million Credit Facility with a net leverage ratio covenant, defined as net debt divided by EBITDA, set at 2.5 to 1, that is in place when $30.0 million or more has been drawn down on the revolving credit facility. In addition, the applicable margin in the case of LIBOR-based loans was reduced by 1.25% to 2.50% and will range from 2.25% to 2.50% based on the secured net leverage ratio of the Company.

Dividends Declared

On February 14, 2018, the Company declared a quarterly cash dividend of $0.45 per common share to be paid on May 15, 2018 to shareholders of record at the close of business on April 30, 2018. The Company also declared a quarterly cash dividend of $1.8125 per share on the Company's 7.25% mandatory convertible preferred stock to be paid on May 1, 2018 to shareholders of record at the close of business on April 16, 2018.