2.Significant Balance Sheet Components

Accounts Receivable, Net —Accounts receivable, net at September 30, 2019 and December 31, 2018 consisted of the following (in thousands):


	September 30, 2019		December 31, 2018
Accounts receivable - billed	$	42,749	$	60,037
Accounts receivable - unbilled		2,206		1,382
Allowance for doubtful accounts		(391)		(425)
Accounts receivable, net	$	44,564	$	60,994

Property and Equipment —Property and equipment at September 30, 2019 and December 31, 2018 consisted of the following (in thousands):


	September 30, 2019		December 31, 2018
Computers and appliances	$	14,218	$	13,517
Purchased software		4,886		4,711
Furniture and fixtures		1,799		1,695
Leasehold improvements		3,400		3,503
Total property and equipment		24,303		23,426
Accumulated depreciation and amortization		(18,774)		(16,380)
Total property and equipment—net	$	5,529	$	7,046

Prepaid expenses and other current assets at September 30, 2019 and December 31, 2018 included $7.8 million and $3.8 million of prepaid royalties, respectively. Other assets at September 30, 2019 and December 31, 2018 included $3.3 million and $3.4 million of prepaid royalties, respectively. The prepaid royalties were primarily associated with MobileIron Threat Defense.

Accrued Expenses —Accrued expenses at September 30, 2019 and December 31, 2018 consisted of the following (in thousands):


	September 30, 2019		December 31, 2018
Accrued commissions	$	4,567	$	4,398
Accrued stock-settled bonus		5,454		9,355
Employee Stock Purchase Plan liability		890		1,923
Other accrued payroll-related expenses		3,113		3,630
Accrued royalties		2,091		3,596
Other accrued liabilities		4,337		4,445
Total accrued expenses	$	20,452	$	27,347