Financial Instruments - Schedule of Cash, Cash Equivalents, Short-Term Investments and Restricted Cash and Investments Unrealized Loss Positions (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Fair Value
Unrealized Losses Less than 12 Months	$ 104,676
Unrealized Losses 12 Months or Greater	64,398
Total	169,074
Gross Unrealized Loss
Unrealized Losses Less than 12 Months	(104)
Unrealized Losses 12 Months or Greater	(347)
Total	(451)
U.S. Treasury and agencies
Fair Value
Unrealized Losses Less than 12 Months, available for sale	25,704
Unrealized Losses 12 Months or Greater, available for sale	3,983
Total, available for sale	29,687
Gross Unrealized Loss
Unrealized Losses Less than 12 Months, available for sale	(7)
Unrealized Losses 12 Months or Greater, available for sale	(17)
Total, available for sale	(24)
Mutual funds
Fair Value
Unrealized Losses Less than 12 Months, trading	4,859
Unrealized Losses 12 Months or Greater, trading	9,007
Total, trading	13,866
Gross Unrealized Loss
Unrealized Losses Less than 12 Months, trading	(78)
Unrealized Losses 12 Months or Greater	(205)
Total, trading	(283)
Government-sponsored enterprises
Fair Value
Unrealized Losses Less than 12 Months, available for sale	0
Unrealized Losses 12 Months or Greater, available for sale	10,953
Total, available for sale	10,953
Gross Unrealized Loss
Unrealized Losses Less than 12 Months, available for sale	0
Unrealized Losses 12 Months or Greater, available for sale	(41)
Total, available for sale	(41)
Corporate notes and bonds
Fair Value
Unrealized Losses Less than 12 Months, available for sale	67,984
Unrealized Losses 12 Months or Greater, available for sale	40,455
Total, available for sale	108,439
Gross Unrealized Loss
Unrealized Losses Less than 12 Months, available for sale	(15)
Unrealized Losses 12 Months or Greater, available for sale	(84)
Total, available for sale	(99)
Mortgage backed securities - residential
Fair Value
Unrealized Losses Less than 12 Months, available for sale	6,129
Unrealized Losses 12 Months or Greater, available for sale	0
Total, available for sale	6,129
Gross Unrealized Loss
Unrealized Losses Less than 12 Months, available for sale	(4)
Unrealized Losses 12 Months or Greater, available for sale	0
Total, available for sale	$ (4)

Available-for-sale and Trading Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss

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