Employee Benefit Plans	12 Months Ended
	Dec. 31, 2020
Postemployment Benefits [Abstract]
Employee Benefit Plans	Employee Benefit PlansThe Employee Thrift Plan (“Plan”) provides that all employees of Horizon with the requisite hours of service are eligible for the Plan. The Plan permits voluntary employee contributions and Horizon may make discretionary matching and profit sharing contributions. Each eligible employee is vested according to a schedule based upon years of service. Employee voluntary contributions are vested at all times. The Bank’s expense related to the Plan totaled approximately $1.4 million in 2020, $1.2 million in 2019 and $942,000 in 2018.The Plan owns a total of 851,388 shares of Horizon’s stock or 1.9% of the outstanding shares as of December 31, 2020.The Pentegra Defined Benefit Plan (“Pentegra Plan”), acquired from the Peoples acquisition, was terminated in April of 2020. The Pentegra Plan was transferred into annuity contracts and will no longer be administered by the Company. The termination liability was $3.4 million, which the Company recorded a $2.9 million withdrawal liability resulting in an additional termination expense in 2020 of $460,000.