Cash, Cash Equivalents, and Investments

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



	December 31,
	2018		2017
Cash	$	104,655	$	97,951
Money market instruments	3,557		8,631
Cash and cash equivalents	108,212		106,582
Treasury bills	198,477		150,371
Corporate bonds	137,871		47,395
Asset-backed securities	78,407		59,203
Sovereign bonds	8,101		21,579
Municipal bonds	4,492		8,805
Agency bonds	—		10,608
Short-term investments	427,348		297,961
Corporate bonds	162,566		296,014
Asset-backed securities	53,631		71,727
Treasury bills	32,760		23,459
Sovereign bonds	6,316		13,147
Agency bonds	5,921		14,890
Municipal bonds	845		4,204
Long-term investments	262,039		423,441
	$	797,599	$	827,984

The Company’s cash balance included foreign bank balances totaling $67,502,000 and $66,777,000 as of December 31, 2018 and 2017, respectively.

Treasury bills consist of debt securities issued by the U.S. government; corporate bonds consist of debt securities issued by both domestic and foreign companies; asset-backed securities consist of debt securities collateralized by pools of receivables or loans with credit enhancement; sovereign bonds consist of direct debt issued by foreign governments; municipal bonds consist of debt securities issued by state and local government entities; agency bonds consist of domestic or foreign obligations of government agencies and government-sponsored enterprises that have government backing.

The following table summarizes the Company’s available-for-sale investments as of December 31, 2018 (in thousands):



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Short-term:
Treasury bills	$	198,512	$	38	$	(73	)	$	198,477
Corporate bonds	138,219		27		(375		)	137,871
Asset-backed securities	78,628		15		(236		)	78,407
Sovereign bonds	8,135		—		(34		)	8,101
Municipal bonds	4,492		—		—			4,492
Long-term:
Corporate bonds	163,847		107		(1,388		)	162,566
Asset-backed securities	53,693		55		(117		)	53,631
Treasury bills	32,722		51		(13		)	32,760
Sovereign bonds	6,286		30		—			6,316
Agency bonds	5,930		—		(9		)	5,921
Municipal bonds	855		—		(10		)	845
	$	691,319	$	323	$	(2,255	)	$	689,387

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, 2018 (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
Corporate bonds	$	145,596	$	(1,268	)	$	99,886	$	(495	)	$	245,482	$	(1,763	)
Treasury bills	114,836		(73		)	$	13,850	(13		)	128,686		(86		)
Asset-backed securities	47,762		(91		)	44,585		(262		)	92,347		(353		)
Sovereign bonds	3,492		(4		)	4,609		(30		)	8,101		(34		)
Agency Bonds	5,920		(9		)	—		—			5,920		(9		)
Municipal bonds	1,302		—			845		(10		)	2,147		(10		)
	$	318,908	$	(1,445	)	$	163,775	$	(810	)	$	482,683	$	(2,255	)

As of December 31, 2018, 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 $669,000 in 2018, $929,000 in 2017, and $292,000 in 2016, and gross realized losses on the sale of debt securities totaling $168,000 in 2018, $100,000 in 2017, and $101,000 in 2016. 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, 2018 (in thousands):



	<1 Year		1-2 Years		2-3 Years		3-4 Years		4-5 Years		5-7 Years		Total
Corporate bonds	$	137,871	$	81,921	$	56,459	$	20,060	$	4,126	$	—	$	300,437
Treasury bills	198,477		32,760		—		—		—		—		231,237
Asset-backed securities	78,407		27,665		7,715		11,004		3,416		3,831		132,038
Sovereign bonds	8,101		6,316		—		—		—		—		14,417
Agency bonds	—		—		—		5,921		—		—		5,921
Municipal bonds	4,492		845		—		—		—		—		5,337
	$	427,348	$	149,507	$	64,174	$	36,985	$	7,542	$	3,831	$	689,387