Marketable Securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Adjusted Cost	$ 58,606	$ 91,359
Unrealized Gains	1,009	411
Unrealized Losses	(28)	(1,180)
Fair Value	59,587	90,590
Equity securities
Debt Securities, Trading, and Equity Securities, FV-NI [Abstract]
Adjusted Cost	4,200	10,101
Unrealized Gains	0	0
Unrealized Losses	(24)	(956)
Fair Value	4,176	9,145
Money market and mutual funds
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Adjusted Cost	43,306	52,733
Unrealized Gains	785	316
Unrealized Losses	0	(53)
Fair Value	44,091	52,996
Corporate bonds
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Adjusted Cost	4,190	6,411
Unrealized Gains	69	7
Unrealized Losses	(1)	(79)
Fair Value	4,258	6,339
Government securities - U.S.
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Adjusted Cost	5,217	12,714
Unrealized Gains	129	66
Unrealized Losses	(2)	(79)
Fair Value	5,344	12,701
Other fixed-income securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Adjusted Cost	1,693	9,400
Unrealized Gains	26	22
Unrealized Losses	(1)	(13)
Fair Value	$ 1,718	$ 9,409

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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