The following is a summary of fixed assets as of December 31, 2024 and 2023 (in thousands):


	December 31,
	2024			2023
Office equipment	$	213,083		$	356,707
Internally developed software		103,351			85,993
Leasehold improvements		89,382			141,585
Building		81,207			80,771
Aircraft engine operating leases		4,886			2,370
		491,909			667,426
Accumulated depreciation and amortization		(298,753	)		(475,898	)
	$	193,156		$	191,528

For the years ended December 31, 2024, 2023, and 2022, depreciation and amortization totaled $62.4 million, $60.5 million, and $50.6 million, respectively.

As of December 31, 2024, the Company had a total lease portfolio of 18 aircraft engines with a net book value of $121.3 million. The aircraft engines were purchased by the Company, through its subsidiaries, during 2024. See Note 29 for additional information.

During the third quarter of 2024, the Company transferred 22 aircraft engines with a net book value of $152.1 million from aircraft engine operating leases included in fixed assets, net to aircraft engines held for sale, included in other assets in the accompanying consolidated statements of financial condition. The Company ceases recognition of depreciation expense once an aircraft engine is classified as held for sale.

During the year ended December 31, 2024, the Company sold 11 aircraft engines with a net book value of $59.4 million and recognized a gain from the sale of $46.5 million, which is included in principal transactions in the consolidated statements of operations.

Lease income, included in other income in the consolidated statements of operations, was $25.3 million for the year ended December 31, 2024.