Data from IPREO confirms that. Cambridge Investment Research Advisors held 713,459 shares of MARA as of 9/30/15. All purchased during the third quarter.
They are an investment advisor-manager of managers—they outsource a portion of their stock selection to external, third party managers, so technically they have a passive investment orientation.
$3.4B equity under management. They are the number 2 holder now with just under 5% of MARA shares outstanding.