Leases

We lease land, office and warehouse space, and certain office equipment under operating leases that expire at various dates through November 30, 2060.

Rent expense for our operating leases was $4.9 million, $4.2 million and $4.0 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Estimated future minimum non-cancelable operating lease payments at December 31, 2018 were as follows:



(In thousands)	Amount
2019	$	5,887
2020	5,620
2021	5,510
2022	4,707
2023	2,718
Thereafter	2,863
Total operating lease commitments	$	27,305

Non-level Rents and Lease Incentives

Some of our leases are subject to rent escalations. For these leases, we recognize rent expense for the total contractual obligation utilizing the straight-line method over the lease term, ranging from 48 months to 125 months. The related short-term liability is recorded in other accrued liabilities (see Note 11) and the related long term liability is recorded in other long-term liabilities. The total liability related to rent escalations was $1.1 million and $1.2 million at December 31, 2018 and 2017, respectively.

The lease agreements for our offices in Santa Ana, California and Scottsdale, Arizona contain allowances for moving expenses and tenant improvements aggregating $1.8 million. These moving and tenant improvement allowances are recorded within other accrued liabilities and other long-term liabilities, depending on the short-term or long-term nature, and are being amortized as a reduction of rent expense over the related lease term.

Rental Costs During Construction

Rental costs associated with operating leases incurred during a construction period are expensed.

Prepaid Land Lease

We operate one factory within the PRC on which the land is leased from the government as of December 31, 2018. This land lease was prepaid to the PRC government at the time our subsidiary occupied the land. We have obtained a land-use right certificate for the land pertaining to this factory.

The factory is located in the city of Yangzhou in the Jiangsu province. The remaining net book value of this prepaid lease was $2.5 million on December 31, 2018, and will be amortized on a straight-line basis over the remaining term of approximately 40 years. The buildings located on this land had a net book value of $18.2 million on December 31, 2018 and will be depreciated over a remaining weighted average period of 21 years.

The remaining net book value of this prepaid land lease is included within prepaid expenses and other current assets and other assets, depending on the short-term or long-term nature.