NOTE I — ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES AND OTHER LIABILITIES

Accrued expenses and other current liabilities consist of:


	As of December 31,
(in thousands)	2018		2017

Patient prepayments, deposits and refunds payable	$	24,563	$	30,194
Insurance and self-insurance accruals		8,886		8,901
Accrued sales taxes and other taxes		6,810		6,335
Accrued professional fees		3,751		11,612
Derivative liability		724		—
Accrued interest payable		332		845
Other current liabilities		6,717		8,421
Total	$	51,783	$	66,308

Patient prepayment deposits and refunds includes funds received for devices not yet delivered to a patient and refunds for overpayments. Accrued insurance primarily relates to accruals for estimated losses for certain self-insured risks including property, professional liability, and general liability, and employee health care costs. Accrued professional fees primarily relate to accruals for professional accounting and legal fees. Taxes primarily includes accrued sales tax liabilities and other taxes payable. Derivative liability relates to our cash flow hedge; refer to Note O - “Derivative Financial Instruments.” Other current liabilities are primarily related to accruals for deferred revenue and warranty liabilities.

Other liabilities consist of:


	As of December 31,
(in thousands)	2018		2017

Supplemental executive retirement plan obligations	$	20,195	$	21,842
Long-term insurance accruals		8,713		9,531
Deferred tenant improvement allowances		8,570		7,361
Unrecognized tax benefits, and related interest and penalties		5,458		5,219
Deferred rent		4,455		4,909
Derivative liability		3,134		—
Other		1,045		1,391
Total	$	51,570	$	50,253

Supplemental executive retirement plan obligations includes obligations due on both the Defined Benefit Supplemental Executive Retirement Plan (“DB SERP”) and DC SERP. See Note K - “Employee Benefits” within these consolidated financial statements. Unrecognized tax benefits represent the difference between tax positions that we expect to take, or take on our income tax returns and the benefit we recognize on our financial statements. Deferred tenant improvement allowance represents deferred credits associated with receiving lease incentives. Deferred rent represents net deferred credits associated with recognizing rent expense on a straight-line basis for property operating leases whose lease payments escalate over the life of the lease. Both deferred credits are recognized as reductions of rent expense over the term of the associated lease. Derivative liability relates to our cash flow hedge; refer to Note O - “Derivative Financial Instruments.” Other includes asset retirement obligations, which is the liability to return a leased building to the state before it was occupied, fair market value lease differential liability, build-to-suit tenant interest accrual, and other long-term accrued expenses.