Cash, Cash Equivalents, and Investments

Cash, cash equivalents, and investments consisted of the following (in thousands):



	December 31,
	2017		2016
Cash	$	97,951	$	77,307
Money market instruments	8,631		2,334
Cash and cash equivalents	106,582		79,641
Treasury bills	150,371		67,175
Asset-backed securities	59,203		69,614
Corporate bonds	47,395		141,188
Sovereign bonds	21,579		7,298
Agency bonds	10,608		2,903
Municipal bonds	8,805		6,517
Euro liquidity fund	—		46,499
Short-term investments	297,961		341,194
Corporate bonds	296,014		169,952
Asset-backed securities	71,727		26,946
Treasury bills	23,459		92,280
Agency bonds	14,890		10,339
Sovereign bonds	13,147		23,585
Municipal bonds	4,204		1,233
Long-term investments	423,441		324,335
	$	827,984	$	745,170

The Company’s cash balance included foreign bank balances totaling $66,777,000 and $68,076,000 as of December 31, 2017 and 2016, respectively.

Treasury bills consist of debt securities issued by the U.S. government; asset-backed securities consist of debt securities collateralized by pools of receivables or loans with credit enhancement; corporate bonds consist of debt securities issued by both domestic and foreign companies; sovereign bonds consist of direct debt issued by foreign governments; agency bonds consist of domestic or foreign obligations of government agencies and government-sponsored enterprises that have government backing; municipal bonds consist of debt securities issued by state and local government entities; and the Euro liquidity fund invests in a portfolio of investment-grade bonds. The Euro liquidity fund is denominated in Euros, and the remaining securities are denominated in U.S. Dollars.

The following table summarizes the Company’s available-for-sale investments as of December 31, 2017 (in thousands):



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Short-term:
Treasury bills	$	150,726	$	—	$	(355	)	$	150,371
Asset-backed securities	59,267		8		(72		)	59,203
Corporate bonds	47,391		29		(25		)	47,395
Sovereign bonds	21,607		1		(29		)	21,579
Agency bonds	10,600		8		—			10,608
Municipal bonds	8,805		—		—			8,805
Long-term:
Corporate bonds	295,427		981		(394		)	296,014
Asset-backed securities	71,801		30		(104		)	71,727
Treasury bills	23,567		—		(108		)	23,459
Agency bonds	14,878		14		(2		)	14,890
Sovereign bonds	13,171		35		(59		)	13,147
Municipal bonds	4,220		—		(16		)	4,204
	$	721,460	$	1,106	$	(1,164	)	$	721,402

The following table summarizes the Company’s gross unrealized losses and fair values for available-for-sale investments in an unrealized loss position as of December 31, 2017 (in thousands):



	Unrealized Loss Position For Less than 12 Months					Unrealized Loss Position For Greater than 12 Months					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Treasury bills	$	145,051	$	(403	)	$	25,176	$	(60	)	$	170,227	$	(463	)
Corporate bonds	126,659		(241		)	19,324		(178		)	145,983		(419		)
Asset-backed securities	75,842		(171		)	2,698		(5		)	78,540		(176		)
Sovereign bonds	3,809		(4		)	17,941		(84		)	21,750		(88		)
Agency Bonds	5,928		(2		)	—		—			5,928		(2		)
Municipal bonds	4,203		(16		)	—		—			4,203		(16		)
	$	361,492	$	(837	)	$	65,139	$	(327	)	$	426,631	$	(1,164	)

As of December 31, 2017, the Company did not recognize any other-than-temporary impairment of these investments. In its evaluation, management considered the type of security, the credit rating of the security, the length of time the security has been in a loss position, the size of the loss position, our intent and ability to hold the security to expected recovery of value, and other meaningful information. The Company does not intend to sell, and is unlikely to be required to sell, any of these available-for-sale investments before its effective maturity or market price recovery.

The Company recorded gross realized gains on the sale of debt securities totaling $929,000 in 2017, $292,000 in 2016, and $549,000 in 2015, and gross realized losses on the sale of debt securities totaling $100,000 in 2017, $101,000 in 2016, and $205,000 in 2015. These gains and losses are included in "Investment income" on the Consolidated Statement of Operations. Prior to the sale of these securities, unrealized gains and losses for these debt securities, net of tax, are recorded in shareholders’ equity as other comprehensive income (loss).

The following table summarizes the effective maturity dates of the Company’s available-for-sale investments as of December 31, 2017 (in thousands):



	<1 Year		1-2 Years		2-3 Years		3-4 Years		4-5 Years		5-7 Years		Total
Corporate bonds	$	47,395	$	154,541	$	77,772	$	26,545	$	32,352	$	4,804	$	343,409
Treasury bills	150,371		23,459		—		—		—		—		173,830
Asset-backed securities	59,203		46,985		13,456		3,262		2,334		5,690		130,930
Sovereign bonds	21,579		4,580		8,567		—		—		—		34,726
Agency bonds	10,608		8,962		—		—		5,928		—		25,498
Municipal bonds	8,805		2,854		1,350		—		—		—		13,009
	$	297,961	$	241,381	$	101,145	$	29,807	$	40,614	$	10,494	$	721,402