Athenahealth Inc. has closed the deal to purchase the Arsenal on the Charles in Watertown for $168.5 million.

The company, which provides electronic record and billing systems to hospitals, bought the 29-acre parcel from Harvard University. Athenahealth was already leasing the space as its headquarters, but the purchase will allow executives to expand the business in coming years.

Athenahealth entered into a new $325 million senior credit facility with a term of five years, comprised of a $200 million unsecured-term loan and a $125 million unsecured revolving credit facility to finance the purchase and refinance existing debt. Bank of America Merrill Lynch and TD Bank were the lead lenders for the financing.

Steve Cook of Avison Young represented Athenahealth in the purchase of the 311 Arsenal St. property, which comprises 11 buildings with 760,000 square feet of commercial space. Portions of the property are 200 years old.

Athenahealth’s decision last year to buy its own real estate instead of continuing to lease was far from an anomaly. In 2012, CRE users that bought their own space to occupy helped drive a 22 percent increase in overall office sales in the Greater Boston market over the previous year, with owner-occupiers accounting for 2.4 million square feet of total sales transactions, according to Cushman & Wakefield.

In 2011, owner-occupied office sales volume in Greater Boston was piddling in comparison, totaling only 300,000 square feet from three transactions.