Marketable Securities Marketable Securities - Schedule of Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 62,151	$ 90,590
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	735
1-5 Years	2,929
5-10 Years	0
Greater than 10 Years	0
Fair Value	3,664	6,339
Government securities - U.S.
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	0
1-5 Years	4,798
5-10 Years	0
Greater than 10 Years	436
Fair Value	5,234	12,701
Other fixed-income securities
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	426
1-5 Years	1,756
5-10 Years	0
Greater than 10 Years	0
Fair Value	2,182	$ 9,409
Debt Securities, Excluding Money Market Funds, Available For Sale
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	1,161
1-5 Years	9,483
5-10 Years	0
Greater than 10 Years	436
Fair Value	$ 11,080

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