	December 31, 2020			December 31, 2019
Computer and communications equipment	$	92,565		$	95,115
Software, including software development costs		259,439			235,230
Leasehold improvements and other fixed assets		120,951			116,231
		472,955			446,576
Less: accumulated depreciation and amortization		(258,173	)		(241,735	)
Fixed assets, net	$	214,782		$	204,841

Depreciation expense was $24.1 million, $21.5 million and $19.5 million for the years ended December 31, 2020, 2019 and 2018, respectively. Depreciation is included as part of “Occupancy and equipment” in the Company’s consolidated statements of operations.

The Company has approximately $5.9 million and $6.4 million of asset retirement obligations related to certain of its leasehold improvements as of December 31, 2020 and 2019, respectively. The associated asset retirement cost is capitalized as part of the carrying amount of the long-lived asset. The liability is discounted and accretion expense is recognized using the credit adjusted risk-free interest rate in effect when the liability was initially recognized.

For the years ended December 31, 2020, 2019 and 2018, software development costs totaling $54.0 million, $48.8 million and $49.9 million, respectively, were capitalized. Amortization of software development costs totaled $31.8 million, $28.6 million and $24.7 million for the years ended December 31, 2020, 2019 and 2018, respectively. Amortization of software development costs is included as part of “Occupancy and equipment” in the Company’s consolidated statements of operations.

Impairment charges of $7.0 million, $4.5 million and $1.1 million were recorded for the years ended December 31, 2020, 2019 and 2018, respectively, related to the evaluation of capitalized software projects for future benefit and for fixed assets no longer in service. Impairment charges related to capitalized software and fixed assets are reflected in “Occupancy and equipment” in the Company’s consolidated statements of operations.