4. Financial Instruments

The Company elected to invest a portion of its cash assets in conservative, income earning, liquid investments effective September 2015. Cash equivalents and investments, all of which are classified as available-for-sale securities, consisted of the following:


	March 31, 2016								December 31, 2015
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized (Loss)		Estimated Fair Value		Amortized Cost		Gross Unrealized Gain		Gross Unrealized (Loss)		Estimated Fair Value
	(in thousands)
Money market deposits	$	8,263	$	—	$	—	$	8,263	$	5,966	$	—	$	—	$	5,966
U.S. Treasury securities		102,950		183		(37)		103,096		104,537		1		(725)		103,813
U.S. agency securities		74,428		228		(40)		74,616		79,491		—		(638)		78,853
Municipal securities		18,824		68		(7)		18,885		18,974		2		(56)		18,920
Total	$	204,465	$	479	$	(84)	$	204,860	$	208,968	$	3	$	(1,419)	$	207,552

Classified as:
Cash equivalents							$	8,263							$	5,966
Short-term investments								196,597								201,586
Total							$	204,860							$	207,552

The Company invests in U.S. Treasuries, U.S. agency and high quality municipal bonds which mature at par and are all paying their coupons on schedule. Thus the Company has determined there is currently no other than temporary impairment of its investments, and will continue to recognize unrealized losses and gains in other comprehensive income (loss). During the three months ended March 31, 2016, the Company had $0.1 million in realized gains and immaterial losses for a total net realized gain of $0.1 million. The Company uses the specific investment identification method to calculate realized gains and losses as well as the amount reclassified out of other comprehensive income to net income. As of March 31, 2016, the Company has 34 investments in an unrealized loss position in its portfolio. The Company earned interest income of $0.4 million during the three months ended March 31, 2016. The following table summarizes the Company’s portfolio of available-for-sale securities by contractual maturity as of March 31, 2016:


	March 31, 2016
	Amortized Cost		Fair Value
	(in thousands)
Less than one year	$	59,489	$	59,464
Greater than one year but less than five years		144,976		145,396
Total	$	204,465	$	204,860