occupancy and depreciation of $5.2 million, $2.7 million, $2.1 million, and $0.9 million, respectively. Our increases in employee compensation, occupancy, depreciation, and other general and administrative costs are primarily related to the Acquisition, including additional headcount, and office space in Indianapolis, Indiana. Our increase in professional fees is primarily related to a payment made to an outside provider that assisted us in obtaining a state tax refund with a favorable tax impact of $5.9 million in the first quarter of 2019 and higher legal fees. Our increase in other general and administrative costs is primarily due to increases in travel costs and increases in contributions made in lieu of state income taxes to school sponsoring organizations from $3.7 million for the nine months ended September 30, 2018 to $4.0 million for the nine months ended in September 30, 2019. Our general and administrative expenses as a percentage of as adjusted non-GAAP net revenue increased by 1.0% to 6.0% for the nine months ended September 30, 2019, from 5.0% for the nine months ended September 30, 2018 due to the increase in professional fees, employee compensation, and office space for Orbis Education, partially offset by our ability to leverage our general and administrative expenses across an increasing revenue base.
Amortization of intangible assets. The amortization of intangible assets for the nine months ended September 30, 2019 was $6.0 million and is related to the Acquisition of Orbis Education, which resulted in the creation of certain identifiable intangible assets that will be amortized over their expected lives.
University related expenses. Our university related expenses for the nine months ended September 30, 2018 were $173.7 million. These expenses represent the costs transferred to the university for the six months ended June 30, 2018 and in the three months ended September 30, 2018 are primarily due to the Company’s Board of Directors modifying the vesting condition for certain restricted stock awards for personnel that would be transferred to GCU, which resulted in $7.9 million of share-based compensation expense, and employer taxes of $0.2 million on such modification. This amount was partially offset by reversals of employee related liabilities totaling $1.5 million that were not part of the transferred asset for the Transaction.
Loss on transaction. The loss on transaction for the nine months ended September 30, 2019 was $4.0 million due to transaction costs related to the Acquisition of Orbis Education. Our loss on transaction expenses for the nine months ended September 30, 2018 was $17.6 million due to transactions costs of $5.0 million and an asset impairment of $3.0 million. In addition, the Company transferred to GCU cash of $9.6 million to fund a deferred compensation plan for GCU employees who were formerly GCE employees and that held unvested restricted stock of GCE that was forfeited upon the Transaction.
Interest income on Secured Note. Interest income on the Secured Note (as defined below) for the nine months ended September 30, 2019 was $44.4 million, an increase of $31.2 million, as compared to interest income on Secured Note of $13.2 million for the nine months ended September 30, 2018. This increased as a result of the Transaction with GCU that commenced on July 1, 2018, the Company recognizes interest income on its Secured Note with GCU including borrowings made for capital expenditures, earning interest at 6%, with monthly interest payments.
Interest expense. Interest expense was $8.4 million for the nine months ended September 30, 2019, an increase of $7.4 million, as compared to interest expense of $1.0 million for the nine months ended September 30, 2018. The increase in interest expense is primarily due to the Acquisition of Orbis Education, which resulted in a $190.1 million increase in our outstanding credit facility, a slightly higher interest rate on the credit facility, additional fees on the revolving credit facility, and lower capitalized interest as compared to the same period in the prior year.
Investment interest and other. Investment interest and other for the nine months ended September 30, 2019 was $4.0 million, an increase of $1.1 million, as compared to $2.9 million in the nine months ended September 30, 2018.
Income tax expense. Income tax expense for the nine months ended September 30, 2019 was $40.8 million, an increase of $1.1 million, or 2.6%, as compared to income tax expense of $39.7 million for the nine months ended September 30, 2018. This increase is the result of an increase in our taxable income between periods, offset by a decrease in our effective tax rate. Our effective tax rate was 18.3% during the nine months ended September 30, 2019 compared to 20.6% during the nine months ended September 30, 2018. The decrease in the effective tax rate resulted from an agreement with the Arizona Department of Revenue regarding previously filed refund claims related to income tax obligations for prior calendar years, which resulted in a favorable tax impact of $5.9 million recorded as a discrete