Marketable Securities Marketable Securities - Schedule of Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 59,587	$ 90,590
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	556
1-5 Years	3,360
5-10 Years	342
Greater than 10 Years	0
Fair Value	4,258	6,339
Government securities - U.S.
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	0
1-5 Years	4,600
5-10 Years	0
Greater than 10 Years	744
Fair Value	5,344	12,701
Other fixed-income securities
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	49
1-5 Years	1,669
5-10 Years	0
Greater than 10 Years	0
Fair Value	1,718	$ 9,409
Debt Securities, Excluding Money Market Funds, Available For Sale
Debt Securities, Available-for-sale [Line Items]
Less than 1 Year	605
1-5 Years	9,629
5-10 Years	342
Greater than 10 Years	744
Fair Value	$ 11,320

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