Marketable Investment Securities (Tables)

12 Months Ended

Dec. 31, 2019

Our marketable investment securities portfolio consists of the following debt and equity instruments:



	As of December 31,
	2019		2018

Marketable investment securities:
Debt securities:
Corporate bonds	$	577,570	$	1,735,653
Other debt securities	335,580		464,997
Total debt securities	913,150		2,200,650
Equity securities	35,566		90,976
Total marketable investment securities	948,716		2,291,626
Less: Restricted marketable investment securities	8,093		9,474
Total marketable investment securities	$	940,623	$	2,282,152

Schedule of Unrealized Gains (Losses) on Available for Sale Securities

The following table is a summary of our available-for-sale debt securities:



	Amortized		Unrealized					Estimated
	Cost		Gains		Losses			Fair Value

As of December 31, 2019
Corporate bonds	$	567,926	$	518	$	(2	)	$	568,442
Other debt securities	335,572		8		—			335,580
Total available-for-sale debt securities	$	903,498	$	526	$	(2	)	$	904,022
As of December 31, 2018
Corporate bonds	$	1,689,093	$	318	$	(1,896	)	$	1,687,515
Other debt securities	464,993		7		(3		)	464,997
Total available-for-sale debt securities	$	2,154,086	$	325	$	(1,899	)	$	2,152,512

Schedule of Fair Value Measurements

Our marketable investment securities are summarized in the table below. Certain of our investments in debt and equity instruments have historically experienced volatility. As of December 31, 2019 and 2018, we did not have any investments that were categorized within Level 3 of the fair value hierarchy.



	As of December 31,
	2019						2018
	Level 1		Level 2		Total		Level 1		Level 2		Total

Debt securities:
Corporate bonds	$	—	$	577,570	$	577,570	$	—	$	1,735,653	$	1,735,653
Other debt securities	8,093		327,487		335,580		9,474		455,523		464,997
Total debt securities	8,093		905,057		913,150		9,474		2,191,176		2,200,650
Equity securities	27,933		7,633		35,566		85,298		5,678		90,976
Total marketable investment securities	$	36,026	$	912,690	$	948,716	$	94,772	$	2,196,854	$	2,291,626