	December 31, 2019			December 31, 2018
Computer and communications equipment	$	95,115		$	140,451
Software, including software development costs		235,230			194,470
Leasehold improvements and other fixed assets		116,231			127,349
		446,576			462,270
Less: accumulated depreciation and amortization		(241,735	)		(305,101	)
Fixed assets, net	$	204,841		$	157,169

Depreciation expense was $21.5 million, $19.5 million and $20.2 million for the years ended December 31, 2019, 2018 and 2017, respectively. Depreciation is included as part of “Occupancy and equipment” in the Company’s consolidated statements of operations.

The Company has approximately $6.4 million of asset retirement obligations related to certain of its leasehold improvements as of December 31, 2019. 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, 2019, 2018 and 2017, software development costs totaling $48.8 million, $49.9 million and $33.2 million, respectively, were capitalized. Amortization of software development costs totaled $28.6 million, $24.7 million and $19.0 million for the years ended December 31, 2019, 2018 and 2017, 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 $4.5 million, $1.1 million and $4.1 million were recorded for the years ended December 31, 2019, 2018 and 2017, 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.