Senator Investment Group LP, the hedge-fund firm backed by Blackstone Group LP, disclosed a 6.3 percent holding in Radian Group Inc., becoming the latest asset manager to wager on a housing recovery by taking a stake in the mortgage insurer.

Senator has 12 million shares in Radian, the New York-based firm said in a regulatory filing. That’s the second-largest holding in the Philadelphia-based insurer, trailing a 9 percent stake held by Fidelity Investments, according to data compiled by Bloomberg.