Investment Securities Table (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Current	$ 36,960	$ 10,061
Debt Securities, Available-for-sale, Noncurrent	2,922	14,579
Debt Securities, Available-for-sale, Amortized Cost	39,882	24,640
Debt Securities, Available-for-sale, Unrealized Loss	0	0
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value	36,960	10,061
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value	2,922	14,579
Debt Securities, Available-for-sale	39,882	24,640
Available-for-sale Debt Security Current [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Available-for-sale Debt Security Noncurrent [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0	$ 0

Amortized cost of 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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