Knight Capital Group Inc. announced Monday it has reached an agreement to buy Astor Asset Management LLC, a Chicago-based money manager that specializes in macro-economic strategy and ETF portfolio construction.

Jersey-City based Knight will pay approximately $20 million in cash and stock for Astor when the acquisition is completed in the fourth quarter.

Thomas M. Joyse, Knight's chairman and chief executive officer, said in a press release that Astor has grown rapidly by inexpensively offering active management through exchange-traded funds.

"Astor assets under management in the separately managed accounts and new mutual fund have increased substantially in the past few years. I believe we can help Astor get to the next level while creating a foundation for asset management that contributes stable, recurring revenues to Knight," he said.

Astor, which was founded in 2001, utilizes proprietary macroeconomic models to construct portfolios of exchange-traded funds that are offered through advisors within separately-managed accounts and the Astor Long/Short ETF Mutual Fund.

Astor has 13 employees and approximately $560 million in assets under management.

When the deal closes, Astor would operate as a wholly-owned operating subsidiary of Knight.