4. Cash, cash equivalents, restricted cash, and available for sale marketable securities

Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase. Investments consist of securities with original maturities greater than 90 days when purchased. The Company classifies these investments as available-for-sale and records them at fair value in the accompanying condensed consolidated balance sheets. Unrealized gains or losses are included in accumulated other comprehensive loss. Premiums or discounts from par value are amortized to investment income over the life of the underlying investment.

The Company classifies marketable debt securities with a remaining maturity when purchased of greater than three months as available‑for‑sale. Marketable debt securities with a remaining maturity date greater than one year and marketable equity securities are classified as non‑current where the Company has the intent and ability to hold these securities for at least the next 12 months. Available‑for‑sale debt securities are maintained by an investment manager and consist of U.S. Treasury notes. In 2016, the Company invested in a supplier and received common stock and warrants to purchase common stock in that entity. The common stock is included in non-current marketable securities and the warrants are included in non-current assets.

All available‑for‑sale securities are carried at fair value with the unrealized gains and losses included in other comprehensive loss as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense. Realized gains and losses are determined using the specific identification method and are included in other income (expense). If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other‑than‑temporary” and, if so, recognizes the unrealized loss through a charge to the Company’s statement of operations and comprehensive loss. No other than temporary losses have been recognized.

Cash, cash equivalents, and marketable securities included the following at March 31, 2018 and December 31, 2017:


	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
	(in thousands)
As of March 31, 2018
Money market funds included in cash and cash equivalents	$	139,269	$	—	$	—	$	139,269
Marketable securities:
U.S. Treasury notes		77,862		—		35		77,827
Equity securities		1,220		100		—		1,320
Total marketable securities	$	79,082	$	100	$	35	$	79,147
Total money market funds and marketable securities	$	218,351	$	100	$	35	$	218,416
As of December 31, 2017
Money market funds included in cash and cash equivalents	$	30,469	$	—	$	—	$	30,469
Marketable securities:
U.S. Treasury notes		137,560		—		38		137,522
Equity securities		1,220		—		120		1,100
Total marketable securities	$	138,780	$	—	$	158	$	138,622
Total money market funds and marketable securities	$	169,249	$	—	$	158	$	169,091

All of the Company’s marketable debt securities at March 31, 2018, have a contractual maturity of one year or less.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the statement of financial position that sum to the total of the same such amounts shown in the statement of cash flows:


	As of March 31,
	2018		2017
	(in thousands)
Cash and cash equivalents	$	140,371	$	43,604
Restricted cash included in deposits and other noncurrent assets		735		735
Total cash, cash equivalents, and restricted cash	$	141,106	$	44,339