4. Cash, Cash Equivalents and Investments

As of March 31, 2016, and December 31, 2015, we had invested our excess cash balances primarily in money market funds, and a corporate equity security. Our 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, we have not experienced credit losses on investments in these instruments, and we do not require collateral for our investment activities.



Summary of Cash and Available-For-Sale Securities	Adjusted Cost		Unrealized Gains		Unrealized Losses		Estimated Fair Value		Cash and Cash Equivalents		Short-Term Investments
(In thousands)
March 31, 2016
Cash	$	91,104	$	—	$	—	$	91,104	$	91,104	$	—
Money market funds	199,546		—		—		199,546		199,546		—
Corporate securities	663		643		—		1,306		—		1,306
Total	$	291,313	$	643	$	—	$	291,956	$	290,650	$	1,306

December 31, 2015
Cash	$	124,082	$	—	$	—	$	124,082	$	124,082	$	—
Money market funds	94,801		—		—		94,801		94,801		—
Corporate securities	799		670		—		1,469		—		1,469
Total	$	219,682	$	670	$	—	$	220,352	$	218,883	$	1,469

For the three months ended March 31, 2016 and December 31, 2015, we recognized approximately $136,000 and $997,000, on sales of available-for-sale securities.

The unrealized gain on investments included in "Other comprehensive income (loss), net of tax" was approximately $418,000 and $435,000 as of March 31, 2016, and December 31, 2015, respectively.