4. Cash, Cash Equivalents and Short-term Investments

As of September 30, 2017, and December 31, 2016, the Company had invested its excess cash balances primarily in cash, money market funds and commercial paper. The Company’s securities are classified as available-for-sale and are carried at estimated fair value, with unrealized gains and losses reported in “Accumulated other comprehensive income” in stockholders’ equity, net of estimated taxes. See Note 3 for fair value measurement information. The cost of securities sold is based on the specific identification method. To date, the Company has not experienced credit losses on investments in these instruments, and it does not require collateral for its investment activities.

The following tables summarize the Company’s cash and available-for-sale securities’ amortized cost, gross unrealized gains, gross unrealized losses, and fair value by significant investment category reported as cash and cash equivalents, or short-term investments as of September 30, 2017, and December 31, 2016:



							Reported as:
	Amortized Cost		Unrealized Gains		Estimated Fair Value		Cash and Cash Equivalents		Short-Term Investments
(In thousands)
September 30, 2017
Cash	$	495,380	$	—	$	495,380	$	495,380	$	—
Money market funds	14,705		—		14,705		14,705		—
Commercial paper	2,060		—		2,060		—		2,060
Corporate securities	3,352		997		4,349		—		4,349
Total	$	515,497	$	997	$	516,494	$	510,085	$	6,409

December 31, 2016
Cash	$	147,150	$	—	$	147,150	$	147,150	$	—
Money market funds	4		—		4		4		—
Commercial paper	19,987		—		19,987		—		19,987
Total	$	167,141	$	—	$	167,141	$	147,154	$	19,987

The unrealized gains on investments included in "Other comprehensive income (loss), net of tax" was approximately $648,000 and zero as of September 30, 2017, and December 31, 2016, respectively.